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Page No 15.13:

Question 1:

The number of telephone calls received at an exchange per interval for 250 successive one-minute intervals are given in the following frequency table:
 

No. of calls (x): 0 1 2 3 4 5 6
No. of intervals (f): 15 24 29 49 54 43 39

Compute the mean number of calls per intervals.

Answer:

Let the assume mean be.

We know that mean,

Here, we have .

Putting the values in the formula, we get


   

Hence, the mean number of calls per interval is 3.54.

Page No 15.13:

Question 2:

Five coins were simultaneously tossed 1000 times, and at each toss the number of heads was observed. The number of tosses during which 0, 1, 2, 3, 4 and 5 heads were obtained are shown in the table below: Find the mean number of heads per toss
 

No. of heads per toss (x): 0 1 2 3 4 5
No. of tosses (f): 38 144 342 287 164 25

Answer:

Let the assume mean be.

We know that mean

Now, we have

Putting the values above in formula, we have


Hence, the mean number of heads per toss is 2.47.

Page No 15.13:

Question 3:

The following table given the number of branches and number of plants in the garden of a school.

No. of branches (x): 2 3 4 5 6
No. of plants (f): 49 43 57 38 13

Answer:

Let the assume mean be.

We know that mean,

Now, we have

Putting the values in the above formula, we get


   
   

Hence, the mean number of branches per plant is approximately 3.62.

Page No 15.13:

Question 4:

The following table gives the number of children of 150 families in a village
 

No. of children (x): 0 1 2 3 4 5
No. of families (f): 10 21 55 42 15 7

Find the average number of children per family

Answer:

Let the assume mean be.

We know that mean,

Now, we have

Putting the values above in formula, we get



Hence, the average number of children per family is 2.35.

Page No 15.13:

Question 5:

The marks obtained out of 50, by 102 students in a Physics test are given in the frequency table below:
 

Marks (x): 15 20 22 24 25 30 33 38 45
Frequency (f): 5 8 11 20 23 18 13 3 1

Find the average number of marks.

Answer:

Let the assume mean be.

We know that mean,

Now, we have .

Putting the values in the above formula, we get



Hence, the average number of marks is 26.08.

Page No 15.13:

Question 6:

The number of students absent in a class were recorded every day for 120 days and the information is given in the following frequency table:
 

No. of students absent (x): 0 1 2 3 4 5 6 7
No. of days (f): 1 4 10 50 34 15 4 2

Find the mean number of students absent per day.

Answer:

Let the assume mean be.

We know that mean,

Now, we have .

Putting the values in the above formula,


    
  

Hence, the mean number of students absent per day is approximately 3.53.

Page No 15.13:

Question 7:

In the first proof reading of a book containing 300 pages the following distribution of misprints was obtained:
 

No. of misprints per page (x): 0 1 2 3 4 5
No. of pages (f): 154 95 36 9 5 1

Find the average number of misprints per page.

Answer:

Let the assume mean be.

We know that mean,

Now, we have .

Putting the values in above formula, we have

   

Hence, the mean number of students absent per day is 0.73.

Page No 15.13:

Question 8:

The following distribution gives the number of accidents met by 160 workers in a factory during a month.
 

No. of accidents (x): 0 1 2 3 4
No. of workers (f): 70 52 34 3 1

Find the average number of accidents per worker.

Answer:

Let the assume mean be.

We know that mean,

Now, we have .

Putting the values in the above formula, we get


  

Hence, the average number of accidents per worker is 0.83.



Page No 15.14:

Question 9:

Find the mean from the following frequency distribution of marks at a test in statistics:
 

Marks (x): 5 10 15 20 25 30 35 40 45 50
No. of students (f): 15 50 80 76 72 45 39 9 8 6

Answer:

Let the assumed mean beand .

We know that mean,

Now, we have.

Putting the values in the above formula, we get


Hence, the mean marks is 22.075.



Page No 15.22:

Question 1:

The following tables gives the distribution of total household expenditure (in rupees) of manual workers in a city.

Expenditure
(in rupees) (xi)
Frequency
(fi)
Expenditure
(in rupees) (xi)
Frequency
(fi)
100-150
150-200
200-250
250-300
24
40
33
28
300-350
350-400
400-450
450-500
30
22
16
7

Find the average expenditure (in rupees) per household

Answer:

Given:

Let the assumed mean be A = 275 and h = 50.

We know that mean,

Now, we have.

Putting the values in the above formula, we get


   

Hence, the average expenditureper household is 266.25.

Page No 15.22:

Question 2:

A survey was conducted by a group of students as a part of their environment awareness programme, in which they collected the following data regarding the number of a plants in 20 houses in a locality. Find the mean number of plants per house.
 

Number of plants: 0-2 2-4 4-6 6-8 8-10 10-12 12-14
Number of houses: 1 2 1 5 6 2 3

Which method did you use for finding the mean, and why?

Answer:

We may prepare the table as shown:

We know that mean,
                                  
Hence, mean = 8.1

Direct method is easier than other methods. Therefore, we used direct method.

Page No 15.22:

Question 3:

Consider the following distribution of daily wages of 50 workers of a factory.
 

Daily wages (in Rs.) 100-120 120-140 140-160 160-180 180-200
Number of workers 12 14 8 6 10

Find the mean daily wages of the workers of the factory by using an appropriate method.

Answer:

Let the assumed mean be A = 120 and h = 20.

We know that mean,

Now, we have .

Putting the values in the above formula, we have


   

Hence, the mean daily wage of the workers is Rs 145.20.

Page No 15.22:

Question 4:

Thirty women were examined in a hospital by a doctor and the number of heart beats per minute recorded and summarised as follows. Find the mean heat beats per minute for these women, choosing a suitable method.

Number of heart beats per minute: 65-58 68-71 71-74 74-77 77-80 80-83 83-86
Number of women: 2 4 3 8 7 4 2

Answer:

Let the assumed mean be A = 75.5 and h = 3.

No. of Heart Beats per Min: Mid Value xi No. of Women fi: di=xi-A ui=1h×di fiui
65-68 66.5 2 -9 -3 -6
68-71 69.5 4 -6 -2 -8
71-74 72.5 3 -3 -1 -3
74-77 75.5 = A 8 0 0 0
77-80 78.5 7 3 1 7
80-83 81.5 4 6 2 8
83-86 84.5 2 9 3 6
    fi=30     fiui=4

We know that mean,

Now, we have.

Putting the values in the above formula, we have


  

Hence, the mean heart beats per minute for women is 75.9.

Page No 15.22:

Question 5:

Find the mean of each of the following frequency distributions :
 

Class interval: 0-6 6-12 12-18 18-24 24-30
Frequency: 6 8 10 9 7

Answer:

Let the assumed mean be A = 15 and h = 6.

We know that mean,

Now, we have.

Putting the values in the above formula, we get


  

Hence, the mean is 15.45.

Page No 15.22:

Question 6:

Find the mean of each of the following frequency distributions :
 

Class interval: 50-70 70-90 90-110 110-130 130-150 150-170
Frequency: 18 12 13 27 8 22

Answer:

Let the assumed mean be A = 100 and h = 20.

We know that mean

Now we have

Putting the values in the above formula, we get


Hence, the mean is 112.20.



Page No 15.23:

Question 7:

Find the mean of each of the following frequency distributions :
 

Class interval: 0−8 8−16 16−24 24−32 32−40
Frequency: 6 7 10 8 9

Answer:

Let the assumed mean be A = 20 and h = 8.

We know that mean,

Now, we have.

Putting the values in the above formula, we get


   

Hence, the mean is 21.4.

Page No 15.23:

Question 8:

Find the mean of each of the following frequency distributions :
 

Class interval: 0−6 6−12 12−18 18−24 24−30
Frequency: 7 5 10 12 6

Answer:

Let the assumed mean be A = 15 and h = 6.

We know that mean,

Now, we have.

Putting the values in the above formula, we get


   

Hence, the mean is 15.75.

Page No 15.23:

Question 9:

Find the mean of each of the following frequency distributions :
 

Class interval: 0−10 10−20 20−30 30−40 40−50
Frequency: 9 12 15 10 14

Answer:

Let the assumed mean be A = 25 and h = 10.

We know that mean,

Now, we have.

Putting the values in the above formula, we have


   

Hence, the mean is 26.333.

Page No 15.23:

Question 10:

Find the mean of each of the following frequency distributions :
 

Class interval: 0−8 8−16 16−24 24−32 32−40
Frequency: 5 9 10 8 8

Answer:

Let the assumed mean be A = 20 and h = 8.

We know that mean,

Now, we have.

Putting the values in the above formula, we have


  

Hence, the mean is 21.

Page No 15.23:

Question 11:

Find the mean of each of the following frequency distributions :
 

Class interval: 0−8 8−16 16−24 24−32 32−40
Frequency: 5 6 4 3 2

Answer:

Let the assumed mean be A = 20 and h = 8.

We know that mean,

Now, we have.

Putting the values in the above formula, we get

 
  

Hence, the mean is 16.4.

Page No 15.23:

Question 12:

Find the mean of each of the following frequency distributions :
 

Class interval: 10−30 30−50 50−70 70−90 90−110 110−130
Frequency: 5 8 12 20 3 2

Answer:

Let the assumed mean be A = 60 and h = 20.

We know that mean,

Now, we have.

Putting the values in the above formula, we have


  

Hence, the mean is 65.6.

Page No 15.23:

Question 13:

Find the mean of each of the following frequency distributions :
 

Class interval: 25−35 35−45 45−55 55−65 65−75
Frequency: 6 10 8 12 4

Answer:

Let the assumed mean be A = 50 and h = 10.

We know that mean,

Now, we have.

Putting the values in the above formula, we have


Hence, the mean is 49.5.

Page No 15.23:

Question 14:

Find the mean of each of the following frequency distributions :
 

Classes: 25−29 30−34 35−39 40−44 45−49 50−54 55−59
Frequency: 14 22 16 6 5 3 4

Answer:

The given series is an inclusive series. Firstly, make it an exclusive series.

Class Interval Mid-Value(xi) Frequency(fi) di=xi-A   =xi-42 ui=dih=di5 fiui
24.5-29.5 27 14 −15 −3 −42
29.5-34.5 32 22 −10 −2 −44
34.5-39.5 37 16 −5 −1 −16
39.5-44.5 A = 42 6 0 0 0
44.5-49.5 47 5 5 1 5
49.5-54.5 52 3 10 2 6
54.5-59.5 57 4 15 3 12
    fi=70     fiui=-79

Let the assumed mean be A = 42 and h = 5.

We know that mean,

Now, we have.

Putting the values in the above formula, we have

   

Hence, the mean is 36.357.

Page No 15.23:

Question 15:

For the following distribution, calculate mean using all suitable methods:
 

Size of item: 1−4 4−9 9−16 16−27
Frequency: 6 12 26 20

Answer:

Direct Method:

We may prepare the table as shown:

We know that mean,
                                   

Hence, the mean is 13.25.

Short-Cut Method:

We may prepare the table as shown:
 

Size of Item Mid value(xi) di=xi-A   =xi-12.5 Frequency(fi)        fidi      
1–4 2.5 −10 6 −60
4–9 6.5 −6 12 −72
9–16 12.5 = A 0 26 0
16–27 21.5 9 20 180
      N = fi=64 fidi=48

Let the assumed mean be A = 12.5.

We know that mean, X=A+fidifi
                                   =12.5+4864=12.5+0.75=13.25

Hence, the mean is 13.25.

Step-deviation method cannot be used to evaluate the mean of the distribution as the width of the class intervals are not equal. Here, h is not fixed.

Page No 15.23:

Question 16:

The weekly observations on cost of living index in a certain city for the year 2004 − 2005 are given below. Compute the weekly cost of living index.
 

Cost of living Index Number of Students Cost of living Index Number of Students
1400−1500
1500−1600
1600−1700
5
10
20
1700−1800
1800−1900
1900−2000
9
6
2

Answer:

Let the assumed mean be A = 1650 and h = 100.

We know that mean,

Now, we have.

Putting the values in the above formula, we have


   

Hence, the mean is 1663.46.

Page No 15.23:

Question 17:

The following table shows the marks scored by 140 students in an examination of a certain paper.
 

Marks: 0−10 10−20 20−30 30−40 40−50
Number of students: 20 24 40 36 20

Calculate the average marks by using all the three methods: direct method, assumed mean deviation and shortcut method.

Answer:

We may prepare the table as shown:

(i) Direct method
We know that mean,
                                    =3620140=25.857

Hence, the mean is 25.857.

(ii) Short-cut method

Let the assumed mean A = 25.

We know that mean,
                                   

Hence, the mean is 25.857.

(iii) Step deviation method

Let the assumed mean A = 25 and h = 10.

We know that mean,  
                                   

Hence, the mean is 25.857.

Page No 15.23:

Question 18:

The mean of the following frequency distribution is 62.8 and the sum of all the frequencies is 50. Compute the missing frequency f1 and f2.
 

Class: 0−20 20−40 40−60 60−80 80−100 100−120
Frequency: 5 f1 10 f2 7 9

Answer:

It is given that mean = 62.8 and .

Let the assumed mean A = 50 and h = 20.


             .....(1)

We know that mean,

Now, we have , , .

Putting the values in the above formula, we have

            .....(2)

Putting the value of in (2), we get


                                    

Putting the value of in (1), we get

Hence, the missing frequency f1 = 8 and f2 = 12.



Page No 15.24:

Question 19:

The following distribution shows the daily pocket allowance given to the children of a multistorey building. The average pocket allowance is Rs 18.00. Find the missing frequency.
 

Class: 11−13 13−15 15−17 17−19 19−21 21−23 23−25
Frequency: 7 6 9 13 5 4

Answer:

Given: Mean = 18

Suppose the missing frequency is x.

Let the assumed mean A = 18 and h = 2.

We know that mean,

Now, we have,,.

Putting the values in the above formula, we have

18=18+2x-20x+442x-20x+44=0x-20=0x=20

Thus, the missing frequency is 20.

Page No 15.24:

Question 20:

If the mean of the following distribution is 27, find the value of p.
 

Class: 0−10 10−20 20−30 30−40 40−50
Frequency: 8 p 12 13 10

Answer:

Given: Mean = 27

Let the assumed mean A = 25 and h = 10.

We know that mean,

Now, we have,,

Putting the values in the above formula, we have

 
    

Thus, the value of p is 7.

Page No 15.24:

Question 21:

In a retail market, fruit vendors were selling mangoes kept in packing boxes. These boxes contained varying number of mangoes. The following was the distribution of mangoes according to the number of boxes.

Number of mangoes: 50−52 53−55 56−58 59−61 62−64
Number of boxes: 15 110 135 115 25

Find the mean number of mangoes kept in a packing box. Which method of finding the mean did you choose?

Answer:

The given series is an inclusive series. Firstly, make it an exclusive series.

Class Interval Mid-Value(xi) Frequency(fi) di=xi-A   =xi-57 ui=dih=di3 fiui
49.5-52.5 51 15 −6 −2 −30
52.5-55.5 54 110 −3 −1 −110
55.5-58.5 57 135 0 0 0
58.5-61.5 60 115 3 1 115
61.5-64.5 63 25 6 2 50
    fi=400     fiui=25

Let the assumed mean be A = 57 and h = 3.

We know that mean,

Now, we have.

Putting the values in the above formula, we have


   

Hence, the mean is approximately 57.19.

Page No 15.24:

Question 22:

The table below shows the daily expenditure on food of 25 household in a locality

Daily expenditure (in Rs): 100−150 150−200 200−250 250−300 300−350
Number of households: 4 5 12 2 2

Find the mean daily expenditure on food by a suitable method.

Answer:

Let the assumed mean a = 225 and h = 50.
 

Daily expenditure (in Rs) fi xi di = xi − 225 fiui
100−150 4 125 − 100 − 2 − 8
150−200 5 175 − 50 − 1 − 5
200−250 12 225 0 0 0
250−300 2 275 50 1 2
300−350 2 325 100 2 4
Total fi=25       fiui=− 7

Now,

Therefore, mean daily expenditure on food is Rs 211.

Page No 15.24:

Question 23:

To find out the concentration of SO2 in the air (in parts per million, i.e., ppm), the data was collected for 30 localities in a certain city and is presented below:
 

Concentration of SO2 (in ppm) Frequency
0.00−0.04
0.04−0.08
0.08−0.12
0.12−0.16
0.16−0.20
0.20−0.24
4
9
9
2
4
2

Find the mean of concentration of SO2 in the air.

Answer:

Let the assumed mean A = 0.1 and h = 0.04.

We know that mean,

Now, we have.

Putting the values in the above formula, we have

 
   =0.10+0.04130×-1=0.10-0.0430=0.10-0.001=0.099

Hence, the mean concentration of SO2 in the air is 0.099 ppm.

Page No 15.24:

Question 24:

A class teacher has the following absentee record of 40 students of a class for the whole term. Find the mean number of days a student was absent.
 

Number of days: 0−6 6−10 10−14 14−20 20−28 28−38 38−40
Number of students: 11 10 7 4 4 3 1

Answer:

Let the assume mean A = 17.

We know that mean,

Now, we have.

Putting the values in the above formula, we have


   

Hence, the mean number of days a student was absent is 12.475.

Page No 15.24:

Question 25:

The following table gives the literacy rate (in percentage) of 35 cities. Find the mean literacy rate.

Literacy rate (in %): 45−55 55−65 65−75 75−85 85−95
Number of cities: 3 10 11 8 3

Answer:

Let the assumed mean A = 70 and h = 10.

We know that mean,

Now, we have

Putting the values in the above formula, we have
 

   

Hence, the mean literacy rate is approximately 69.43%.

Page No 15.24:

Question 26:

 The following is the cumulative frequency distribution ( of less than type ) of 1000 persons each of age 20 years and above . Determine the mean age .

Age below (in years) :    30      40      50      60    70    80 

Number of persons:       100     220   350  750   950   1000  

Answer:


Let the assumed mean A = 55 and h = 10.

Marks Mid-Value Frequency ui=xi-5510 fiui
20–30 25 100 −3 −300
30–40 35 120 −2 −240
40–50 45 130 −1 −130
50–60 55 400 0 0
60–70 65 200 1 200
70–80 75 50 2 100
    N = 1000   fiui=-370

We know that mean,
Now, we have N=fi=1000, h=10, A=55, fiui=-370
X¯=55+1011000×-370=55-3.7=51.3 years



Page No 15.25:

Question 27:

If the mean of the following frequency distribution is 18 , find the missing frequency .

Class interval :          11-13     13-15    15-17    17-19    19-21    21-23     23-25

Frequency:                  3              6            9          13        f              5            4

Answer:

It is given that mean of the data is 18.
Let the assumed mean A = 18 and h = 2.

Marks Mid-Value(xi) Frequency ui=xi-182 fiui
11–13 12 3 −3 −9
13–15 14 6 −2 −12
15–17 16 9 −1 −9
17–19 18 13 0 0
19–21 20 f 1 f
21–23 22 5 2 10
23–25 24 4 3 12
    N = 40 + f   fiui=-8+f

We know that mean,
Now, we have N=fi=40+f, h=2, A=18, fiui=-8+f
18=18+2140+f×-8+f0=-16+2f40+f-16+2f=0f=8

Page No 15.25:

Question 28:

Find the missing frequencies in the following distribution , if the sum of the frequencies is 120 and the mean is 50 .
Class:             0-20      20-40       40-60         60-80        80-100

Frequency:     17           f             32              f2             19 

Answer:

It is given that mean of the data is 50.
Let the assumed mean A = 50 and h = 10.

Marks Mid-Value(xi) Frequency ui=xi-5020 fiui
0–20 10 17 −2 −34
20–40 30 f1 −1 f1
40–60 50 32 0 0
60–80 70 f2 1 f2
80–100 90 19 2 38
    N = 68 + f1 + f2   fiui=4-f1+f2

We know that mean,
Now, we have N = 68 + f1 + f2, h=20, A=50, fiui=4-f1+f2.
50=50+204-f1+f268+f1+f2f1-f2=4f1=4+f2               .....1
Now, N = 68 + f1 + f2 = 120
f1+f2= 120-68=524+f2+f2=52               Using 1f2=24So,f1=4+24=28

Page No 15.25:

Question 29:

The daily income of a sample of 50 employees are tabulated as follows:
Income  (in ₹):        1-200          201-400          401-600        601-800

No.of employees :     14                15                    14                7

Find the mean daily income of employees.

Answer:


Let the assumed mean A = 500.5 and h = 200.

Marks Mid-Value(xi) Frequency ui=xi-500.5200 fiui
1–200 100.5 14 −2 −28
201–400 300.5 15 −1 −15
401–600 500.5 14 0 0
601–800 700.5 7 1 7
    N = 50   fiui=-36

We know that mean,
Now, we have N=fi=50, h=200, A=500.5, fiui=-36
X¯=500.5+200150×-36=500.5-144=356.5



Page No 15.34:

Question 1:

Following are the lives in hours of 15 pieces of the components of aircraft engine. Find the median:

715, 724, 725, 710, 729, 745, 694, 699, 696, 712, 734, 728, 716, 705, 719

Answer:

First of all arranging the data in ascending order of magnitude, we have

Here,, which is an odd number

Therefore, median is the value of

Page No 15.34:

Question 2:

The following is the distribution of height of students of a certain class in a certain city:
 

Height (in cms): 160−162 163−165 166−168 169−171 172−174
No. of students: 15 118 142 127 18

Find the median height.

Answer:

First we prepare the following cummulative table to compute the median.

Now,

Thus, the cumulative frequency just greater than 210 is 275 and the corresponding class is .

Therefore, is the median class.

We know that,


          
          

Hence, the median height is approximately 167.1 cm.

Page No 15.34:

Question 3:

Following is the distribution of I.Q. of 100 students. Find the median I.Q.
 

I.Q.: 55−64 65−74 75−84 85−94 95−104 105−114 115−124 125−134 135-144
No. of students: 1 2 9 22 33 22 8 2 1

Answer:

Here, the frequency table is given in inclusive form. Transforming the given table into exclusive form and prepare the cumulative frequency table.
 

IQ Frequency(fi) Cummulative Frequency(c.f.)
54.5−64.5 1 1
64.5−74.5 2 3
74.5−84.5 9 12
84.5−94.5 22 34
94.5−104.5 33 67
104.5−114.5 22 89
114.5−124.5 8 97
124.5−134.5 2 99
134.5−144.5 1 100
  N = 100  

Here,

So,

Thus, the cumulative frequency just greater than 50 is 67 and the corresponding class is 94.5−104.5.

Therefore, 94.5−104.5 is the median class.

Here, l = 94.5, f = 33, F = 34 and h = 9

We know that,


=94.5+50-3433×10=94.5+16033=94.5+4.85=99.35

Hence, the median is 99.35.

Page No 15.34:

Question 4:

Calculate the median from the following data:
 

Rent (in Rs.): 15−25 25−35 35−45 45−55 55−65 65−75 75−85 85−95
No. of Houses: 8 10 15 25 40 20 15 7

Answer:

First we prepare the following cummulative table to compute the median.

Here,

So,

Thus, the cumulative frequency just greater than 70 is 98 and the corresponding class is .

Therefore, is the median class.

Here,

We know that

 
           
           

Hence, the median is 58.

Page No 15.34:

Question 5:

Calculate the median from the following data:

Marks below: 10 20 30 40 50 60 70 80
No. of students: 15 35 60 84 96 127 198 250

Answer:

First we prepare the following cummulative table to compute the median.

Here,

So,

Thus, the cumulative frequency just greater than 125 is 127 and the corresponding class is .

Therefore, is the median class.

Here,

We know that


                
            

Hence, the median is 59.35.

Page No 15.34:

Question 6:

Calculate the missing frequency from the following distribution, it being given that the median of the distribution is 24.
 

Age in years: 0−10 10−20 20−30 30−40 40−50
No. of persons: 5 25 ? 18 7

Answer:

Let the frequency of the class 20−30 be.It is given that median is 35 which lies in the class 20−30. So 20−30 is the median class.

Now, lower limit of median class

Height of the class

Frequency of median class

Cumulative frequency of preceding median class

Total frequency

Formula to be used to calculate median,

Where,

- Lower limit of median class

- Height of the class

- Frequency of median class

- Cumulative frequency of preceding median class

- Total frequency

Put the values in the above,

Hence, the required frequency is 25.

Page No 15.34:

Question 7:

The following table gives the frequency distribution of married women by age at marriage:
 

Age
(in years)
Frequency Age
(in years)
Frequency
15−19
20−24
25−29
30−34
35−39
53
140
98
32
12
40−44
45−49
50−54
55−59
60 and above
9
5
3
3
2

Calculate the median and interpret the results.

Answer:

Here, the frequency table is given in inclusive form. So, we first transform it into exclusive form by subtracting and adding h/2 to the lower and upper limits respectively of each class, where h denotes the difference of lower limit of a class and upper limit of the previous class.

We have, N = 357
So, N/2 = 178.5

Thus, the cumulative frequency just greater than 178.5 is 193 and the corresponding class is 19.5−24.5.

Therefore, 19.5−24.5 is the median class.

Here, l = 19.5, f = 140, F = 193 and h = 5

We know that

           =19.5+178.5-53140×5=19.5+125.5140×5=19.5+125.528=546+125.528=23.98

Hence, the median age 23.98 years.

Thus, nearly half the women were married between the age of 19.5 years and 24.5 years.

Page No 15.34:

Question 8:

The following table gives the distribution of the life time of 400 neon lamps:
 

Lite time:
(in hours)
Number of lamps
1500−2000
2000−2500
2500−3000
3000−3500
3500−4000
4000−4500
4500−5000
14
56
60
86
74
62
48

Find the median life.

Answer:

We prepare the cumulative frequency table, as given below.

We have,

So,

Now, the cumulative frequency just greater than 200 is 216 and the corresponding class is .

Therefore, is the median class.

Here,

We know that

 
              
           

Hence, the median life of the lamps is approximately 3406.98 hours.



Page No 15.35:

Question 9:

The distribution below gives the weight of 30 students in a class. Find the median weight of students:
 

Weight (in kg): 40−45 45−50 50−55 55−60 60−65 65−70 70−75
No. of students: 2 3 8 6 6 3 2

Answer:

We prepare the cumulative frequency table, as given below.

We have,

So,

Now, the cumulative frequency just greater than 15 is 19 and the corresponding class is .

Therefore, is the median class.

Here,

We know that


             
           

Hence, the median weight of students is 56.67 kg.

Page No 15.35:

Question 10:

Find the missing frequencies and the median for the following distribution if the mean is 1.46.

No. of accidents: 0 1 2 3 4 5 Total
Frequency: 46 ? ? 25 10 5 200

Answer:

(1) Let the missing frequencies be x and y.

Given:

     .....(1)

We know that mean,  
               

         .....(2)

Solving (1) and (2), we get

Therefore,

Hence, the missing frequencies are 38 and 76.

(2) Calculation of median.

Now, we have.

So,

Thus, the cumulative frequency just greater than 100 is 122 and the value corresponding to 122 is 1.

Hence, the median is 1.

Page No 15.35:

Question 11:

An incomplete distribution is given below :
 

Variable: 10−20 20−30 30−40 40−50 50−60 60−70 70−80
Frequency: 12 30 65 25 18

You are given that the median value is 46 and the total number of items is 230.
(i) Using the median formula fill up missing frequencies.
(ii) Calculate the AM of the completed distribution.

Answer:

(i) Let the missing frequencies be x and y.

First we prepare the following cummulative table.

Here,

So,

It is given that the median is 46.

Therefore, is the median class.

We know that

 
 
 

Also,

Putting the value of x, we get

Hence, the missing frequencies are 34 and 46.

(ii)

We may prepare the table as shown.

We know that mean,

Now, we have.

Putting the values in the above formula, we have


   

Hence, the mean is 45.87.

Page No 15.35:

Question 12:

If the median of the following frequency distribution is 28.5 find the missing frequencies:
 

Class interval: 0−10 10−20 20−30 30−40 40−50 50−60 Total
Frequency: 5 f1 20 15 f2 5 60

Answer:

Given: Median = 28.5

We prepare the cumulative frequency table, as given below.

Now, we have

         .....(1)

Also,

Since the median = 28.5 so the median class is 20−30.

Here,

We know that


Putting the value of in (1), we get

Hence, the missing frequencies are 7 and 8.

Page No 15.35:

Question 13:

The median of the following data is 525. Find the missing frequency, if it is given that there are 100 observation in the data:
 

Class interval Frequency Class interval Frequency
0−100
100−200
200−300
300−400
400−500
2
5
f1
12
17
500−600
600−700
700−800
800−900
900−1000
20
f2
9
7
4

Answer:

Given: Median = 525

We prepare the cumulative frequency table, as given below.

Now, we have

       .....(1)

So,

Since median = 525 so the median class is .

Here,

We know that

 

Putting the value of in (1), we get

Hence, the missing frequencies are 9 and 15.

Page No 15.35:

Question 14:

If the median of the following data is 32.5, find the missing frequencies.
 

Class interval: 0−10 10−20 20−30 30−40 40−50 50−60 60−70 Total
Frequency: f1 5 9 12 f2 3 2 40

Answer:

Given: Median = 32.5

We prepare the cumulative frequency table, as given below.

Now, we have

          .....(1)

Also,

Since median = 32.5 so the median class is .

Here,

We know that

 
 


Putting the value of in (1), we get

Hence, the missing frequencies are 3 and 6.

Page No 15.35:

Question 15:

Compute the median for each of the following data:

(i)

Marks No. of students
Less than 10
Less than 30
Less than 50
Less than 70
Less than 90
Less than 110
Less than 130
Less than 150
0
10
25
43
65
87
96
100

(ii)
Marks No. of students
More than 150
More than 140
More than 130
More than 120
More than 110
More than 100
More than 90
More than 80
0
12
27
60
105
124
141
150

Answer:

(i)

We prepare the cumulative frequency table, as given below.

Now, we have

So,

Now, the cumulative frequency just greater than 50 is 65 and the corresponding class is .

Therefore, is the median class.

Here,

We know that


           
           

Hence, the median is 76.36.

Note: The first class in the table can be omitted also.

(ii)

We prepare the cumulative frequency table, as given below.

Now, we have

So.

Thus, the cumulative frequency just greater than 75 is 105 and the corresponding class is .

Therefore, is the median class.

(Because class interval given in descending order)

We know that


               
              = 120 − 3.333

              = 116.67   (approx)

Hence, the median is 116.67.



Page No 15.36:

Question 16:

A survey regarding the height (in cm) of 51 girls of class X of a school was conducted and the following data was obtained:
 

Height in cm Number of Girls
Less than 140
Less than 145
Less than 150
Less than 155
Less than 160
Less than 165
4
11
29
40
46
51

Find the median height.

Answer:

We prepare the cumulative frequency, table as given below.

Now, we have

So,

Now, the cumulative frequency just greater than 25.5 is 40 and the corresponding class is .

Therefore, is the median class.

We know that

 
           
            = 150 − 1.59
            = 148.41

Hence, the median height is 148.41 cm.

Page No 15.36:

Question 17:

A life insurance agent found the following data for distribution of ages of 100 policy holders. Calculate the median age, if policies are only given to persons having age 18 years onward but less than 60 years.
 

Age in years Number of policy holders
Below 20
Below 25
Below 30
Below 35
Below 40
Below 45
Below 50
Below 55
Below 60
2
6
24
45
78
89
92
98
100

Answer:

We prepare the cumulative frequency, table as given below.

Now, we have

So,

Now, the cumulative frequency just greater than 50 is 78 and the corresponding class is .

Therefore, is the median class.

Here,

We know that

 
             
           

Hence, the median age is 35.76 years.

Page No 15.36:

Question 18:

The length of 40 leaves of a plant are measured correct to the nearest millimeter, and the data obtained is represented in the following table:
 

Length (in mm): 118−126 127−135 136−144 145−153 154−162 163−171 172−180
No. of leaves 3 5 9 12 5 4 2

Find the mean length of leaf.

Answer:

Calculation for mean.

Length (in mm) Mid-Values(xi) Number of Leaves(fi ) fi xi
117.5–126.5 122 3 366
126.5–135.5 131 5 655
135.5–144.5 140 9 1260
144.5–153.5 149 12 1788
153.5–162.5 158 5 790
162.5–171.5 167 4 668
171.5–180.5 176 2 353
    N = 40 fixi=5880

Mean length of the leaf = 1Nfixi=140×5880=147

Calculation for median.

The given series is in inclusive form. Converting it to exclusive form and preparing the cumulative frequency table, we have

Length (in mm) Number of Leaves(fi ) Cumulative Frequency (c.f.)
117.5–126.5 3 3
126.5–135.5 5 8
135.5–144.5 9 17
144.5–153.5 12 29
153.5–162.5 5 34
162.5–171.5 4 38
171.5–180.5 2 40
  N = 40  

Now, we have

So,

Now, the cumulative frequency just greater than 20 is 29 and the corresponding class is 144.5–153.5.

Therefore, 144.5–153.5 is the median class.

Here,

We know that


            =144.5+20-1712×9=144.5+2712=144.5+2.25=146.75  

Hence, the median length of leaf is 146.75 mm.

Disclaimer: If the question asks for the mean length of the leaf, then the answer is 147 mm whereas if the question asks fro the median length of the leaf, then the answer is 146.75 mm, which is same as the answer given in the book.

Page No 15.36:

Question 19:

An incomplete distribution is given as follows:
 

Variable: 0−10 10−20 20−30 30−40 40−50 50 − 60 60 − 70
Frequency: 10 20 ? 40 ? 25 15

You are given that the median value is 35 and the sum of all the frequencies is 170. Using the median formula, fill up the missing frequencies.

Answer:

Let the frequency of the class 20−30 be and that of class 40−50 be. The total frequency is 170. So,

So,           .....(1)

It is given that median is 35 which lies in the class 30-40. So 30-40 is the median class.

Now, lower limit of median class

Height of the class

Frequency of median class

Cumulative frequency of preceding median class

Total frequency

Formula to be used to calculate median,

Where,

- Lower limit of median class

- Height of the class

- Frequency of median class

- Cumulative frequency of preceding median class

- Total frequency

Put the values in the above,

Using equation (1), we have

Therefore,

Page No 15.36:

Question 20:

The median of the distribution given below is 14.4 . Find the values of x and y , if the total frequency is 20.

Class interval:       0-6      6-12         12-18           18-24         24-30

Frequency:              4          x               5                 y                  1

Answer:

The given series is in inclusive form. Converting it to exclusive form and preparing the cumulative frequency table, we have

Class interval Frequency(fi ) Cumulative Frequency(c.f.)
0–6 4 4
6–12 x 4 + x
12–18 5 9 + x
18–24 y 9 + x + y
24–30 1 10 + x + y
  10 + x + y = 20  

Median = 14.4
It lies in the interval 12–18, so the median class is 12–18.
Now, we have
l=12, h=6, f=5, F=4+x, N=20
We know that

14.4=12+6×10-4-x512=36-6x6x=24x=4 
Now,
10 + x + y = 20
x+y=10y=10-4=6

Page No 15.36:

Question 21:

The median of the following data is 50. Find the values of p and q  , if the sum of all  the frequencies is 90 .

Marks:        20-30        30-40       40-50        50-60        60-70         70-80       80-90

Frequency:    p               15            25            20               q                 8              10

Answer:

The given series is in inclusive form. Converting it to exclusive form and preparing the cumulative frequency table, we have

Class interval Frequency(fi ) Cumulative Frequency (c.f.)
20–30   p p
30–40 15 p + 15
40–50 25 p + 40
50–60 20 p + 60
60–70 q p + q + 60
70–80 8 p + q + 68
80–90 10 p + q + 78
  78 + p + q = 90  

Median = 50
It lies in the interval 50–60, so the median class is 50–60.
Now, we have
l=50, h=10, f=20, F=p+40, N=90
We know that

50=50+45-p+4020×100=5-p2p=5And, p+q+78=90 p+q=12q=12-5=7



Page No 15.45:

Question 1:

Find the mode of the following data:

(i) 3, 5, 7, 4, 5, 3, 5, 6, 8, 9, 5, 3, 5, 3, 6, 9, 7,4
(ii) 3, 3, 7, 4, 5, 3, 5, 6, 8, 9, 5, 3, 5, 3, 6, 9, 7, 4
(iii) 15, 8, 26, 25, 24, 15, 18, 20, 24, 15, 19, 15

Answer:

(i) 3, 5, 7, 4, 5, 3, 5, 6, 8, 9, 5, 3, 5, 3, 6, 9, 7, 4

The frequency table for the given data

Value x 3 4 5 6 7 8 9
Frequency f 4 2 5 2 2 1 2


We observe that the value 5 has the maximum frequency.

Hence, the mode of data is 5.

 

(ii) 3, 3, 7, 4, 5, 3, 5, 6, 8, 9, 5, 3, 5, 3, 6, 9, 7, 4

The frequency table for the given data

Value x 3 4 5 6 7 8 9
Frequency f 5 2 4 2 2 1 2

We observe that the value 3 has the maximum frequency.

Hence, the mode of data is 3.


(iii) 15, 8, 26, 25, 24, 15, 18, 20, 24, 15, 19, 15

The frequency table for the given data

Value x 8 15 18 19 20 24 25 26
Frequency f 1 4 1 1 1 2 1 1

We observe that the value 15 has the maximum frequency.

Hence, the mode of data is 15.

Page No 15.45:

Question 2:

The shirt sizes worn by a group of 200 persons, who bought the shirt from a store, are as follows:

Shirt Size: 37 38 39 40 41 42 43 44
Number of persons: 15 25 39 41 36 17 15 12

Find the modal shirt size worn by the group.

Answer:

 

Shirt Size 37 38 39 40 41 42 43 44
Number of persons 15 25 39 41 36 17 15 12


Here, shirt size 40 has the maximum number of persons.

Hence, the mode shirt size is 40.

Page No 15.45:

Question 3:

Find the mode of the following distribution.

(i)

Class-interval: 0−10 10−20 20−30 30−40 40−50 50−60 60−70 70−80
Frequency: 5 8 7 12 28 20 10 10

(ii)
Class-interval: 10−15 15−20 20−25 25−30 30−35 35−40
Frequency: 30 45 75 35 25 15

(iii)
Class-interval: 25−30 30−35 35−40 40−45 45−50 50−55
Frequency: 25 34 50 42 38 14

Answer:

(i) Here, maximum frequency is 28 so the modal class is 40−50.

Therefore,

(ii) Here, maximum frequency is 75 so the modal class is 20−25.

Therefore,

(iii) Here, maximum frequency is 50 so the modal class is 35−40.

Therefore,

Page No 15.45:

Question 4:

Compare the modal ages of two groups of students appearing for an entrance test:
 

Age (in years): 16−18 18−20 20−22 22−24 24−26
Group A: 50 78 46 28 23
Group B: 54 89 40 25 17

Answer:

Age (in years) Group ‘A’ Group ‘B’
16–18  50 54
18–20  78 89
20–22  46 40
22–24 28 25
24–25 23 17

For group “A”

The maximum frequency is 78 so the modal class is 18–20.

Therefore,

For group “B”

The maximum frequency 89 so modal class 18–20.

Therefore,

Thus, the modal age of group A is 18.93 years whereas the modal age of group B is 18.83 years.



Page No 15.46:

Question 5:

The marks in science of 80 students of class X are given below: Find the mode of the marks obtained by the students in science.
 

Marks: 0−10 10−20 20−30 30−40 40−50 50−60 60−70 70−80 80−90 90−100
Frequency: 3 5 16 12 13 20 5 4 1 1

Answer:

Marks 0−10 10−20 20−30 30−40 40−50 50−60 60−70 70−80 80−90 90−100
Frequency 3 5 16 12 13 20 5 4 1 1

Here, the maximum frequency is 20 so the modal class is 50−60.

Therefore,



Now,



Thus, the mode of the marks obtained by the students in science is 53.17.

Page No 15.46:

Question 6:

The following is the distribution of height of students of a certain class in a certain city:
 

Height (in cms): 160−162 163−165 166−168 169−171 172−174
Number of students: 15 118 142 127 18

Find the average height of maximum number of students.

Answer:

The given data is an inclusive series. So, firstly convert it into an exclusive series as given below.
 

Height (in cm) 159.5−162.5 162.5−165.5 165.5−168.5 168.5−171.5 171.5−174.5
Number of students 15 118 142 127 18

Here, the maximum frequency is 142 so the modal class is 165.5−168.5.

Therefore,



Now,


          = 165.5 + 1.85
          = 167.35

Thus, the average height of maximum number of students is 167.35 cm.

Page No 15.46:

Question 7:

The following table show the ages of the patients admitted in a hospital during a year:

Age (in years): 5−15 15−25 25−35 35−45 45−55 55−65
Number of patients: 6 11 21 23 14 5

Find the mode and the mean of the data given above. Compare and interpret the two measures of central tendency.

Answer:

Age (in years) 5−15 15−25 25−35 35−45 45−55 55−65
Number of patients 6 11 21 23 14 5

Here, the maximum frequency is 23 so the modal class is 35−45.

Therefore,



Thus, the mode of the ages of the patients is 36.8 years.

Calculation for mean.

Age (in years) Mid-Values(x) Number of patients(f) fx
5−15 10 6 60
15−25 20 11 220
25−35 30 21 630
35−45 40 23 920
45−55 50 14 700
55−65 60 5 300
   

Mean = fxf=283080=35.37

Thus, the mean age of the patients is 35.37 years.

The mean age of the patients is less than the modal age of the patients.

Page No 15.46:

Question 8:

The following data is gives the information on the observed lifetimes (in hours) of 225 electrical components:

Lifetimes (in hours) 0−20 20−40 40−60 60−80 80−100 100−120
No. of components 10 35 52 61 38 29

Determine the modal lifetimes of the components.

Answer:

Lifetimes (in hours) 0−20 20−40 40−60 60−80 80−100 100−120
No. of components 10 35 52 61 38 29

Here, the maximum frequency of electrical components is 61 so the modal class is 60−80.

Therefore,



Thus, the modal lifetimes of the components is 65.625 hours.

Page No 15.46:

Question 9:

The following table gives the daily income of 50 workers of  a factory :

Daily income (in ₹)          100-120        120-140       140-160        160-180       180-200

Number of workers :             12              14                  8                    6                  10

Find the mean, mode and median  of the above data .

Answer:

Let the assumed mean a be 150.

The table for the given data can be drawn as

Class Interval

Number of Workers(fi)

Classmark(xi)

di = xi − 150

fidi

Cumulative Frequency(c.f.)

100−120

12

110

−40

−480

12

120−140

14

130

−20

−280

26

140−160

8

150

0

0

34

160−180

6

170

20

120

40

180−200

10

190

40

400

50

Total

50

   

−240

 

Mean is given by .

Thus, the mean of the given data is 145.2.

It can be seen in the data table that the maximum frequency is 14. The class corresponding to this frequency is 120−140.

∴ Modal class = 120 − 140

Lower limit of modal class (l) = 120

Class size (h) = 140 − 120 = 20

Frequency of modal class (f1) = 14

Frequency of class preceding the modal class (f1) = 12

Frequency of class succeeding the modal class (f1) = 8

Mode is given by

Thus, the mode of the given data is 125.

Here, number of observations (n) = 50

This observation lies in class interval 120−140.

Therefore, the median class is 120−140.

Lower limit of median class (l) = 120

Cumulative frequency of class preceding the median class(c.f.) = 12

Frequency of median class(f) = 14

Median of the data is given by

Thus, the median of the given data is 138.57.

Page No 15.46:

Question 10:

The following distribution gives the state-wise teacher-student ratio in higher secondary schools of India. Find the mode and mean of this data. Interpret, the two measures:
 

Number of students per Teacher Number of States/U.T Number of students per Teacher Number of State/ U.T
15−20
20−25
25−30
30−35
3
8
9
10
35−40
40−45
45−50
50−55
3
0
0
2

Answer:

Number of
students per teacher
Number of
states/U.T. (f
i)

xi

f i xi
15−20 3 17.5 52.5
20−25 8 22.5 180.0
25−30 9 27.5 247.5
30−35 10 32.5 325.0
35−40 3 37.5 112.5
40−45 0 42.5 0
45−50 0 47.5 0
50−55 2 52.5 105.0
   

Here, the maximum frequency is 10 so the modal class is 30−35.

Therefore,



Thus, the mode of the data is 30.6.

Now,
Mean of the data = fixifi=1022.535=29.2
Thus, the mean of the data is 29.2.

The mode of the number of students per teacher in the states is more than the mean of the number of students per teacher in the states.

Page No 15.46:

Question 11:

Find the mean, median and mode of the following data:
 

Classes: 0−50 50−100 100−150 150−200 200−250 250−300 300−350
Frequency: 2 3 5 6 5 3 1

Answer:

Classes Frequency (fi) xi fi xi C.f.
0−50 2 25 50 2
50−100 3 75 225 5
100−150 5 125 625 10
150−200 6 175 1050 16
200−250 5 225 1125 21
250−300 3 275 825 24
300−350 1 325 325 25
    fixi=4225  

Here, the maximum frequency is 6 so the modal class 150−200.

Therefore,

  

Thus, the mean of the data is 169.



Thus, the median of the data is 170.83.

      
           = 175

Thus, the mode of the data is 175.

Page No 15.46:

Question 12:

A student noted the number of cars passing through a spot on a road for 100 periods each of 3 minutes and summarised in the table given below. Find the mode of the data:
 

Number of cars: 0−10 10−20 20−30 30−40 40−50 50−60 60−70 70−80
Frequency: 7 14 13 12 20 11 15 8

Answer:

The given data is shown below.

Number of cars Frequency
0−10 7
10−20 14
20−30 13
30−40 12
40−50 20
50−60 11
60−70 15
70−80 8

Here, the maximum frequency is 20 so the modal class is 40−50.

Therefore,



Mode=l+f-f12f-f1-f2×h=40+20-122×20-12-11×10=40+817×10=40+4.7=44.7

Thus, the mode of the data is 44.7.

Page No 15.46:

Question 13:

The following frequency distribution gives the monthly consumption of electricity of 68 consumers of a locality. Find the median, mean and mode of the data and compare them.

Monthly consumption: (in units) 65−85 85−105 105−125 125−145 145−165 165−185 185−205
No. of consumers: 4 5 13 20 14 8 4

Answer:

The given data is shown below.

Monthly Consumption (in units) No. of consumers (f i) xi fi xi C.f.
65−85 4 75 300 4
85−105 5 95 475 9
105−125 13 115 1495 22
125−145 20 135 2700 42
145−165 14 155 2170 56
165−185 8 175 1400 64
185−205 4 195 780 68
     

Here, the maximum frequency is 20 so the modal class is 125−145.

Therefore,



Thus, the mode of the monthly consumption of electricity is 135.76 units.

Mean = = 137.05

Thus, the mean of the monthly consumption of electricity is 137.05 units.

Here,

Total number of consumers, N = 68 (even)

Then, N2=34

∴ Median


= 137

Thus, the median of the monthly consumption of electricity is 137 units.



Page No 15.47:

Question 14:

100 surnames were randomly picked up from a local telephone directly and the frequency distribution of the number of letters in the English alphabets in the surnames was obtained as follows:
 

Number of letters: 1−4 4−7 7−10 10−13 13−16 16−19
Number of surnames: 6 30 40 16 4 4

Determine the median number of letters in the surnames. Find the mean number of letters in the surnames. Also, fund the modal size of the surnames.

Answer:

Consider the following table.

Number of letters No. of surname xi fi xi C.f.
1−4 6 2.5 15 6
4−7 30 5.5 165 36
7−10 40 8.5 340 76
10−13 16 11.5 184 92
13−16 4 14.5 58 96
16−19 4 17.5 70 100
     

Here, the maximum frequency is 40 so the modal class is 7−10.

Therefore,



Thus, the modal sizes of the surnames is 7.88.



Thus, the mean number of letters in the surnames is 8.32.

Median


Thus, the median number of letters in the surnames is 8.05.

Page No 15.47:

Question 15:

Find the mean, median and mode of the following data:
 

Classes: 0−20 20−40 40−60 60−80 80−100 100−120 120−140
Frequency: 6 8 10 12 6 5 3

Answer:

Consider the following data.

Class Frequency (fi) xi fi xi C.f.
0−20 6 10 60 6
20−40 8 30 240 14
40−60 10 50 500 24
60−80 12 70 840 36
80−100 6 90 540 42
100−120 5 110 550 47
120−140 3 130 390 50
     

Here, the maximum frequency is 12 so the modal class is 60−80.

Therefore,



Thus, the median of the data is 61.66.



Thus, the mean of the data is 62.4.

Mode


Thus, the mode of the data is 65.

Page No 15.47:

Question 16:

The following data gives the distribution of total monthly household expenditure of 200 families of a villages. Find the modal monthly expenditure of the families. Also, find the mean monthly expenditure:
 

Expenditure
(in Rs.)
Frequency Expenditure
(in Rs.)
Frequency
1000−1500
1500−2000
2000−2500
2500−3000
24
40
33
28
3000−3500
3500−4000
4000−4500
4500−5000
30
22
16
7

Answer:

Expenditure Frequency (f i) xi f ixi
1000−1500 24 1250 30000
1500−2000  40 1750 70000
2000−2500 33 2250 74250
2500−3000 28 2750 77000
3000−3500 30 3250 97500
3500−4000 22 3750 82500
4000−4500 16 4250 68000
4500−5000 7 4750 33250
   

Here, the maximum frequency is 40 so the modal class is 1500−2000.

Therefore,


               = 1500 + 347.83
               = Rs 1847.83

Thus, the modal monthly expenditure of the families is Rs 1847.83.

Now,

Mean monthly expenditure of the families



Thus, the mean monthly expenditure of the families is Rs 2662.50.

Page No 15.47:

Question 17:

The given distribution shows the number of runs scored by some top batsmen of the world in one-day international cricket matches.
 

Runs scored Number of batsman Runs scored Number of Batsman
3000−4000
4000−5000
5000−6000
6000−7000
4
18
9
7
7000−8000
8000−9000
9000−10000
10000−11000
6
3
1
1

Find the mode of data.

Answer:

The given data is shown below.

Runs scored Number of batsmen
3000−4000 4
4000−5000 18
5000−6000 9
6000−7000 7
7000−8000 6
8000−9000 3
9000−10000 1
10000−11000 1

Here, the maximum frequency is 18 so the modal class is 4000-5000.

Therefore,



Mode=l+f-f12f-f1-f2×h=4000+18-42×18-4-9×1000=4000+1423×1000=4000+608.7=4608.7


Thus, the mode of the data (or runs scored) is 4608.7.

Page No 15.47:

Question 18:

The frequency distribution table of agriculture holdings in a village is given below:

Area of land (in hectares):       1-3      3-5     5-7     7-9     9-11     11-13

Number of families:                 20       45      80      55        40         12

Find the modal agricultural holdings of the village .

Answer:

The maximum class frequency is 80. The class corresponding to this frequency is 5–7.
So, the modal class is 5–7.
l (the lower limit of modal class) = 5
f1 (frequency of the modal class) = 80
f0 (frequency of the class preceding the modal class) = 45
f2 (frequency of the class succeeding the modal class) = 55
h (class size) = 2
Mode=l+f1-f02f1-f0-f2×h=5+80-452×80-45-55×2=5+3560×2=5+3530=6.2

Hence, the modal agricultural holdings of the village is 6.2 hectares.



Page No 15.48:

Question 19:

 The monthly income of 100 families are given as below :
    Income in ( in  ₹)                                     Number of families

       0-5000                                                           8
5000-10000                                                        26
10000-15000                                                      41
15000-20000                                                      16
20000-25000                                                      3
25000-30000                                                      3
30000-35000                                                      2
35000-40000                                                      1
Calculate the modal income.

Answer:

The maximum class frequency is 41. The class corresponding to this frequency is 10000–15000.
So, the modal class is 10000–15000.
l (the lower limit of modal class) = 10000
f1 (frequency of the modal class) = 41
f0 (frequency of the class preceding the modal class) = 26
f2 (frequency of the class succeeding the modal class) = 16
h (class size) = 5000
Mode=l+f1-f02f1-f0-f2×h=10000+41-262×41-26-16×5000=10000+1540×5000=10000+1875=11875
Thus, the modal income is ₹11875.



Page No 15.5:

Question 1:

Calculate the mean for the following distribution :

x: 5 6 7 8 9
f: 4 8 14 11 3

Answer:

Given:

First of all prepare the frequency table in such a way that its first column consist of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

We know that mean,
                                   

Hence, mean

Page No 15.5:

Question 2:

Find the mean of the following data:

x: 19 21 23 25 27 29 31
f: 13 15 16 18 16 15 13

Answer:

Given:

First of all prepare the frequency table in such a way that its first column consist of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

We know that mean,
                                   

Hence, mean

Page No 15.5:

Question 3:

If the mean of the following data is 20.6. Find the value of p.

x: 10 15 p 25 35
f: 3 10 25 7 5

Answer:

Given:

Also, mean

First of all prepare the frequency table in such a way that its first column consist of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

We know that mean,

By using cross multiplication method,

Hence, p

Page No 15.5:

Question 4:

If the mean of the following data is 15, find p.

x: 5 10 15 20 25
f: 6 p 6 10 5

Answer:

Given:

Also, mean = 15

First of all prepare the frequency table in such a way that its first column consist of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

We know that mean,

By using cross multiplication method


            

Hence, p

Page No 15.5:

Question 5:

Find the value of p for the following distribution whose mean is 16.6.

x: 8 12 15 p 20 25 30
f: 12 16 20 24 16 8 4

Answer:

Given:

Mean = 16.6

First of all prepare the frequency table in such a way that its first column consist of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

We know that mean,

By using cross multiplication method

Hence, p

Page No 15.5:

Question 6:

Find the missing value of p for the following distribution whose mean is 12.58

x: 5 8 10 12 p 20 25
f: 2 5 8 22 7 4 2

Answer:

Given:

Mean

First of all prepare the frequency table in such a way that its first column consist of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

We know that mean,

By using cross multiplication method

Hence, p

Page No 15.5:

Question 7:

Find the missing frequency (p) for the following distribution whose mean is 7.68.

x: 3 5 7 9 11 13
f: 6 8 15 p 8 4

Answer:

Given:

Mean

First of all prepare the frequency table in such a way that its first column consist of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

We know that mean,

By using cross multiplication method,

303+9p=314.88+7.68p9p-7.68p=314.88-303

Hence, p

Page No 15.5:

Question 8:

The following table gives the number of boys of a particular age in a class of 40 students. Calculate the mean age of the students

Age (in years): 15 16 17 18 19 20
No. of students: 3 8 10 10 5 4

Answer:

Given:

First of all prepare the frequency table in such a way that its first column consist of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

We know that mean,
                               

Hence, the mean age of the students



Page No 15.6:

Question 9:

Candidate of four schools appear in a mathematics test. The data were as follows:
 

Schools No. of Candidates Average Score
I
II
III
IV
60
48
Not available
40
75
80
55
50

If the average score of the candidates of all the four schools is 66, find the number of candidates that appeared from school III.

Answer:

Given:

Mean score of the candidates = 66

Let the number of candidates that appeared from school III be x.

First of all prepare the frequency table in such a way that its first column consists of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

We know that mean,
66=10340+55x260

By using cross multiplication method,

Hence, the number of candidates that appeared from school III is 124.

Page No 15.6:

Question 10:

Five coins were simultaneously tossed 1000 times and at each toss the number of heads were observed. The number of tosses during which 0, 1, 2, 3, 4 and 5 heads were obtained are shown in the table below. Find the mean number of heads per toss.

No. of heads per toss No. of tosses
0
1
2
3
4
5
38
144
342
287
164
25
Total 1000

Answer:

Given:

First of all prepare the frequency table in such a way that its first column consist of the numnber of heads per tosses and the second column the corresponding number of tosses .

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denote by and in the third column to obtain.

We know that mean,
                                    =24701000=2.47

Hence, the mean number of heads per toss is 2.47.

Page No 15.6:

Question 11:

The arithmetic mean of the following data is 14. Find the value of k.

xi: 5 10 15 20 25
fi: 7 k 8 4 5

Answer:

Given:

Mean

First of all prepare the frequency table in such a way that its first column consist of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

We know that mean,

By using cross multiplication method,

Hence, k = 6

Page No 15.6:

Question 12:

The arithmetic mean of the following data is 25, find the value of k.

xi: 5 15 25 35 45
fi: 3 k 3 6 2

Answer:

Given:

Mean

First of all prepare the frequency table in such a way that its first column consist of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

We know that mean,

By using cross multiplication method,

Hence, k = 4

Page No 15.6:

Question 13:

If the mean of the following data is 18.75. Find the value of p.

xi: 10 15 p 25 30
fi: 5 10 7 8 2

Answer:

Given:

Mean

First of all prepare the frequency table in such a way that its first column consist of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

We know that mean,

By using cross multiplication method,

Hence, p = 20

Page No 15.6:

Question 14:

Find the value of p, if the mean of the following distribution is 20.

x: 15 17 19 20+p 23
f: 2 3 4 5p 6

Answer:

Given:

Mean

First of all prepare the frequency table in such a way that its first column consist of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

We know that mean,
20=295+5p20+p15+5p

By using cross multiplication method,

5p2+100p+295=300+100p5p2=300-295=5p2=1p=1

Hence, p

Page No 15.6:

Question 15:

Find the missing frequencies in the following frequency distribution if it is known that the mean of the distribution is 50.

x: 10 30 50 70 90  
f: 17 f1 32 f2 19 Total 120

Answer:

Given:

Mean

First of all prepare the frequency table in such a way that its first column consists of the values of the variate and the second column the corresponding frequencies.

Thereafter multiply the frequency of each row with corresponding values of variable to obtain third column containing.

Then, sum of all entries in the column second and denoted by and in the third column to obtain.

Now,

..... (1)

We know that mean,

By using cross multiplication method,


             ..... (2)

Putting the value of from equation (1) in (2), we get

Therefore,

Putting the value of in equation (1), we get

Hence,



Page No 15.62:

Question 1:

Draw an ogive by less than method for the following data:
 

No. of rooms: 1 2 3 4 5 6 7 8 9 10
No. of houses: 4 9 22 28 24 12 8 6 5 2

Answer:

Firstly, we prepare the cumulative frequency table by less than method.

No. of rooms No. of houses (f) Cumulative frequency
1 4 4
2 9 13
3 22 35
4 28 63
5 24 87
6 12 99
7 8 107
8 6 113
9 5 118
10 2 120


Now, plot the less than ogive using the points (1, 4), (2, 13), (3, 35), (4, 63), (5, 87), (6, 99), (7, 107), (8, 113), (9, 118) and (10, 120).
 

Page No 15.62:

Question 2:

The marks scored by 750 students in an examination are given in the form of a frequency distribution table:
 

Marks No. of student Marks No. of students
600−640
640−680
680−720
720−760
16
45
156
284
760−800
800−840
840−880
 
172
59
18
 

Prepare a cumulative frequency table by less than method and draw an ogive.

Answer:

Marks No. of students Marks less then Cumulative frequency Suitable Points
600-640 16 640 16 (640,16)
640-680 45 680 61 (680,61)
680-720 156 720 217 ( 720, 217)
720-760 284 470 501 (760, 501)
760-800 172 800 673 ( 800, 673)
800-840 59 840 732 ( 840,732)
840-880 18 880 750 ( 880,750)

Now, we draw the less than ogive with suitable points.



Page No 15.63:

Question 3:

Draw an ogive to represent the following frequency distribution:

Class-interval: 0−4 5−9 10−14 15−19 20−24
Frequency: 2 6 10 5 3

Answer:

Firstly, prepare the cumulative frequency table.

Class Interval No. of students Less than Cumulative frequency Suitable points
0-4 2 4 2 (4, 2)
5-9 6 9 8 (9, 8)
10-14 10 14 18 (14, 18)
15-19 5 19 23 (19, 23)
20-24 3 24 26 (24, 26)

Now, plot the less than ogive using the suitable points.

Page No 15.63:

Question 4:

The monthly profits (in Rs.) of 100 shops are distributed as follows:
 

Profits per shop: 0−50 50−100 100−150 150−200 200−250 250−300
No. of shops: 12 18 27 20 17 6

Draw the frequency polygon for it.

Answer:

Firstly, we make a cumulative frequency table.

Profit per shop No. of shop More than profit Cumulative frequency Suitable points
0-50 12 0 100 (0, 100)
50-100 18 50 88 (50, 88)
100-150 27 100 70 (100, 70)
150-200 20 150 43 (150, 43)
200-250 17 200 23 (200, 23)
250-300 6 250 6 (250, 6)

Now, plot the frequency polygon (or more than ogive) using suitable points.

Page No 15.63:

Question 5:

The following distribution gives the daily income of 50 workers of a factory:

Daily income in (Rs): 100−120 120−140 140−160 160−180 180−200
Number of workers: 12 14 8 6 10

Convert the above distribution to a less than type cumulative frequency distribution and draw its ogive.

Answer:

Daily income
(in Rs.)
No. of workers (f) Daily income (less than) Cumulative frequency Suitable points
100−120 12 120 12 (120, 12)
120−140 14 140 26 (140, 26)
140−160 8 160 34 (160, 34)
160−180 6 180 40 (180, 40)
180−200 10 200 50 (200, 50)


Now, plot the less than ogive with suitable points.
 

Page No 15.63:

Question 6:

The following table gives production yield per hectare of wheat of 100 farms of a village:
 

Production yield in kg per hectare: 50−55 55−60 60−65 65−70 70−75 75−80  
Number of farms: 2 8 12 24 38 16  

Draw 'less than' ogive and 'more than' ogive.

Answer:

Prepare a table for less than type.
 


Production
yield

No. of
farms
Production
yield
(less than)

 

Cumulative
frequency

Suitable
points
50−55 2 55 2 (55, 2)
55−60 8 60 10 (60, 10)
60−65 12 65 22 (65, 22)
65−70 24 70 46 (70, 46)
70−75 38 75 84 (75, 84)
75−80 16 80 100 (80, 100)

Now, plot the less than ogive using suitable points.

Again, prepare a table for more than type.
 

Production
yield
No. of
farms
Production
yield
(more than)
Cumulative
frequency
Suitable
points
50-55 2 50 100 (50, 100)
55-60 8 55 98 (55, 98)
60-65 12 60 90 (60, 90)
65-70 24 65 78 (65, 78)
70-75 38 70 54 (70, 54)
75-80 16 75 16 (75, 16)


Now, plot the more than ogive with suitable points.


Page No 15.63:

Question 7:

During the medical check up of 35 students of a class, their weights were recorded as follows:
 

Weight (in kg) Number of students
Less than 38
Less than 40
Less than 42
Less than 44
Less than 46
Less than 48
Less than 50
Less than 52
0
3
5
9
14
28
32
35

Draw a less than type ogive for the given data. Hence, obtain the median weight from the graph and verify the result by using the formula.

Answer:

Prepare the table for cumulative frequency for less than type.

Weight
(in kg)
No. of
students
Weight
(less than)
Cumulative
frequency
Suitable
points
36–38 0 38 0 (38, 0)
38–40 3 40 3 (40, 3)
40–42 2 42 5 (42, 5)
42–44 4 44 9 (44, 9)
44–46 5 46 14 (46, 14)
46–48 14 48 28 (48, 28)
48–50 4 50 32 (50, 32)
50–52 3 52 35 (52, 35)

Now, draw the less than ogive using suitable points.



Here, =

From (0, 17.5) draw a line parallel to horizontal axis, which intersects the graph at the point M having x-coordinate as 46.5.

Therefore, the median is 46.5 kg.

Calculation for median using formula.

Now,

So, 46–48 is the median class.

Here,

Hence, both the methods give same result.

Page No 15.63:

Question 8:

The annual rainfall record of a city for 66 days is given in the following table :
Rainfall (in cm ):        0-10      10-20    20-30      30-40      40-50     50-60

Number of days :        22            10        8              15          5              6

Calculate the median rainfall using ogives of more than type and less than type.

Answer:

Prepare a table for less than type.
 

Rainfall
(in cm)
Number of
Days
Rainfall
(Less Than)
Cumulative
Frequency
Suitable
Points
0−10 22 10 22 (10, 22)
10−20 10 20 32 (20, 32)
20−30 8 30 40 (30, 40)
30−40 15 40 55 (40, 55)
40−50 5 50 60 (50, 60)
50−60 6 60 66 (60, 66)

Now, plot the less than ogive using suitable points.


Here, N = 66.
N2=33
In order to find the median rainfall, we first locate the point corresponding to 33rd day on the y-axis. Let the point be P. From this point draw a line parallel to the x-axis cutting the curve at Q. From this point Q, draw a line parallel to the y-axis and meeting the x-axis at the point R. The x-coordinate of R is 21.25.

Thus, the median rainfall is 21.25 cm.

Let us now prepare a table for more than type.

Rainfall (in cm) Number of
Days
Rainfall
(More Than)
Cumulative
Frequency
Suitable
Points
0−10 22 0 66 (0, 66)
10−20 10 10 44 (10, 44)
20−30 8 20 34 (20, 34)
30−40 15 30 26 (30, 26)
40−50 5 40 11 (40, 11)
50−60 6 50 6 (50, 6)

Now, plot the more than ogive with suitable points.


Here, N = 66.
N2=33
In order to find the median rainfall, we first locate the point corresponding to 33rd day on the y-axis. Let the point be P. From this point draw a line parallel to the x-axis cutting the curve at Q. From this point Q, draw a line parallel to the y-axis and meeting the x-axis at the point R. The x-coordinate of R is 21.25.



Thus, the median rainfall is 21.25 cm.



Page No 15.64:

Question 9:

The following table gives the height of trees:
 

Height No. of trees
Less than 7
Less than 14
Less than 21
Less than 28
Less than 35
Less than 42
Less than 49
Less than 56
26
57
92
134
216
287
341
360

Draw 'less than' ogive and 'more than' ogive.

Answer:

Consider the following table.
 

Height (less than) Height-class No. of trees Cumulative frequency Suitable points
7 0-7 26 26 (7, 26)
14 7-14 31 57 (14, 57)
21 14-21 35 92 (21, 92)
28 21-28 42 134 (28, 134)
35 28-35 82 216 (35, 216)
42 35-42 71 287 (42, 287)
49 42-49 54 341 (49, 341)
56 49-56 19 360 (56, 360)

Now, draw the less than ogive using suitable points.

Now, prepare the cumulative frequency table for more than series.

Height No. of trees Height (more than) Cumulative frequency Suitable points
0-7 26 0 360 (0, 360)
7-14 31 7 334 (7, 334)
14-21 35 14 303 (14, 303)
21-28 42 21 268 (21, 268)
28-35 82 28 226 (28, 226)
35-42 71 35 144 (35, 144)
42-49 54 42 73 (42, 73)
49-56 19 49 54 (49, 54)

Now, draw the more than ogive using suitable points.

Page No 15.64:

Question 10:

The annual profits earned by 30 shops of a shopping complex in a locality give rise to the following distribution:
 

Profit (in lakhs in Rs) Number of shops (frequency)
More than or equal to 5
More than or equal to 10
More than or equal to 15
More than or equal to 20
More than or equal to 25
More than or equal to 30
More than or equal to 35
30
28
16
14
10
7
3

Draw both ogives for the above data and hence obtain the median.

Answer:

Firstly, we prepare the cumulative frequency table for less than type.
 


Profit
(In lakh in Rs.)

No. of shops

(frequency)


Profit (less than)

Cumulative
frequency

Suitable
points
5-10 2 10 2 (10, 2)
10-15 12 15 14 (15, 14)
15-20 2 20 16 (20, 16)
20-25 4 25 20 (25, 20)
25-30 3 30 23 (30, 23)
30-35 4 35 27 (35, 27)
35-40 3 40 30 (40, 30)


Again, prepare the cumulative frequency table for more than type.
 


Profit
(In lakh in Rs.)

No. of shops

(frequency)



Profit (more than)

Cumulative
frequency

Suitable
points

5-10 2 5 30 (5, 30)
10-15 12 10 28 (10, 28)
15-20 2 15 16 (15, 16)
20-25 4 20 14 (20, 14)
25-30 3 25 10 (25, 10)
30-35 4 30 7 (30, 7)
35-40 3 35 3 (35, 3)


Now, “more than ogive” and “less than ogive” can be drawn as follows:
 


The x-coordinate of the point of intersection of the “more-than ogive” and “less-than ogive” gives the median of the given distribution..


So, the corresponding median is Rs 17.5 lakh.



Page No 15.65:

Question 1:

Define mean.

Answer:

Mean

The mean of a set of observation is equal to sum of observations divided by the number of observations.

(Where = sum of the observation and n = number of observations)

Page No 15.65:

Question 2:

What is the algebraic sum of deviation of a frequency distribution about its mean?

Answer:

The algebraic sum of deviation of a frequency distribution about its mean is zero.

 

 

Page No 15.65:

Question 3:

Which measure of central tendency is given by the x-coordinate of the point of intersection of the 'more than' ogive and 'less than' ogive?

Answer:

Median

 

Page No 15.65:

Question 4:

What is the value of the median of the data using the graph in the following figure of less than ogive and more than ogive?
 

Answer:

We know that the abscissa of the point of intersection of two ogives gives the median.

From the given figure, it can be seen that both the ogives intersect at the point (4, 15).

∴ Median of the data = 4

Page No 15.65:

Question 5:

Write the empirical relation between mean, mode and median.

Answer:

The empirical relation between mean, median and mode is

Mode = 3 Median − 2 Mean

 

Page No 15.65:

Question 6:

Which measure of central tendency can be determine graphically?

Answer:

Median can be determined graphically.

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Question 7:

Write the modal class for the following frequency distribution:
 

Class-interval: 10−15 15−20 20−25 25−30 30−35 35−40
Frequency: 30 35 75 40 30 15

Answer:

Class Interval 10−15 15−20 20−25 25−30 30−35 35−40
Frequency 30 35 75 40 30 15

Here, the maximum frequency is 75 and the corresponding class-interval is 20−25.

Therefore, 20−25 is the modal class.

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Question 8:

A student draws a cumulative frequency curve for the marks obtained by 40 students of a class as shown below. Find the median marks obtained by the students of the class.
 

Answer:

Here, N = 40

So,

Draw a line parallel to x-axis from the point (0, 20), intersecting the graph at point P.



Now, draw PM from P on the x-axis. The x-coordinate of M gives us the median.

∴ Median = 50

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Question 9:

Write the median class for the following frequency distribution:
 

Class-interval: 0−10 10−20 20−30 30−40 40−50 50−60 60−70 70−80
Frequency: 5 8 7 12 28 20 10 10

Answer:

We are given the following table.

Class Interval Frequency Cumulative Frequency
0−10 5 5
10−20 8 13
20−30 7 20
30−40 12 32
40−50 28 60
50−60 20 80
60−70 10 90
70−80 10 100
  N = 100  

Here, N = 100

N2=50

The cumulative frequency just greater than 50 is 60.

So, the median class is 40−50.



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Question 10:

In the graphical representation of a frequency distribution, if the distance between mode and mean is k times the distance between median and mean, then write the value of k.

Answer:

We have,

Mode = 3 Median − 2 Mean

⇒ Mode − Mean = 3 Median − 3 Mean

⇒ Mode − Mean = 3(Median − Mean)             .....(1)

 It is given that,

 Mode − Mean = k (Median − Mean)               .....(2)

From (1) and (2), we get

k = 3

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Question 11:

Find the class marks of classes 10−25 and 35−55.

Answer:

Class mark of 10−25

Class mark of 35−55

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Question 12:

Write the median class of the following distribution:
 

Class-interval: 0−10 10−20 20−30 30−40 40−50 50−60 60−70
Frequency: 4 4 8 10 12 8 4

Answer:

Consider the following distribution table.

Class Frequency C.F.
0−10 4 4
10−20 4 8
20−30 8 16
30−40 10 26
40−50 12 38
50−60 8 46
60−70 4 50
  N = 50  

Here,

The cumulative frequency just greater than 25 is 26.

So, the median class is 30−40.

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Question 1:

Which of the following is not a measure of central tendency?

(a) Mean
(b) Median
(c) Mode
(d) Standard deviation

Answer:

Standard deviation is not a measure of central tendency.

Hence, correct option is (d).

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Question 2:

The algebraic sum of the deviations of a frequency distribution from its mean is

(a) always positive
(b) always negative
(c) 0
(d) a non-zero number

Answer:

The algebraic sum of the deviations of a frequency distribution from its mean is zero.

Hence, the correct option is (c).

 

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Question 3:

The arithmetic mean of 1, 2, 3, ... , n is

(a) n+12
(b) n-12
(c) n2
(d) n2+1

Answer:

Arithmetic mean of 1, 2, 3, ... , n

=1+2+3+...+nn=nn+12n=n+12


Hence, the correct option is (a).

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Question 4:

For a frequency distribution, mean, median and mode are connected by the relation

(a) Mode = 3 Mean − 2 Median
(b) Mode = 2 Median − 3 Mean
(c) Mode = 3 Median − 2 Mean
(d) Mode = 3 Median + 2 Mean

Answer:

The relation between mean, median and mode is

Mode = 3 Median − 2 Mean

Hence, the correct option is (c).

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Question 5:

Which of the following cannot be determined graphically?

(a) Mean
(b) Median
(c) Mode
(d) None of these

Answer:

‘Mean’ cannot be determined by graphically.

Hence, the correct option is (a).

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Question 6:

The median of a given frequency distribution is found graphically with the help of

(a) Histogram
(b) Frequency curve
(c) Frequency polygon
(d) Ogive

Answer:

The median of a given frequency distribution is found graphically with the help of ‘Ogive’.

Hence, the correct option is (d).

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Question 7:

The mode of a frequency distribution can be determined graphically from

(a) Histogram
(b) Frequency polygon
(c) Ogive
(d) Frequency curve

Answer:

The mode of frequency distribution can be determined graphically from “Histogram”.

Hence, the correct option is (a).

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Question 8:

Mode is

(a) least frequency value
(b) middle most value
(c) most frequent value
(d) None of these

Answer:

Mode is “Most frequent value”.

Hence, the correct option is (c).

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Question 9:

The mean of n observation is X. If the first item is increased by 1, second by 2 and so on, then the new mean is

(a) X+n
(b) X+n2
(c) X+n+12
(d) None of these

Answer:

Let x1, x2,x3,...,xn be the n observations.

Mean=X=x1+x2+...+xnn

x1+x2+x3+...+xn=nX

If the first item is increased by 1, second by 2 and so on.

Then, the new observations are x1+1, x2+2,x3+3,...,xn+n.

New mean = x1+1+ x2+2+x3+3+...+xn+nn
                 =x1+x2+x3+...+xn+1+2+3+...+nn=nX+nn+12n=X+n+12

Hence, the correct answer is (c).

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Question 10:

One of the methods of determining mode is

(a) Mode = 2 Median − 3 Mean
(b) Mode = 2 Median + 3 Mean
(c) Mode = 3 Median − 2 Mean
(d) Mode = 3 Median + 2 Mean

Answer:

We have,

Mode = 3 Median − 2 Mean

Hence, the correct option is (c).

 



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Question 11:

If the mean of the following distribution is 2.6, then the value of y is
 

Variable (x): 1 2 3 4 5
Frequency 4 5 y 1 2

(a) 3
(b) 8
(c) 13
(d) 24

Answer:

Consider the following table.

Variable (x) f fx
1 4 4
2 5 10
3 y 3y
4 1 4
5 2 10
 

Now,


                y = 8

Hence, the correct option is (b).

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Question 12:

The relationship between mean, median and mode for a moderately skewed distribution is

(a) Mode = 2 Median − 3 Mean
(b) Mode = Median − 2 Mean
(c) Mode = 2 Median − Mean
(d) Mode = 3 Median −2 Mean

Answer:

Mode = 3Median − 2Mean

Hence, the correct option is (d).

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Question 13:

The mean of a discrete frequency distribution xi / fi, i = 1, 2, ......, n is given by

(a) Σ fixiΣ fi
(b) 1ni=1nfi xi
(c) i=1n fixii=1n xi
(d) i=1nfixi1=1ni

Answer:

The mean of discrete frequency distribution is

Hence, the correct option is (a).

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Question 14:

If the arithmetic mean of x, x + 3, x + 6, x + 9, and x + 12 is 10, the x =

(a) 1
(b) 2
(c) 6
(d) 4

Answer:

The given observations are x, x + 3, x + 6, x + 9, and x + 12.

x=5x+30, n=5, X=10

Now,

Hence, the correct option is (d).

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Question 15:

If the median of the data: 24, 25, 26, x + 2, x + 3, 30, 31, 34 is 27.5, then x =

(a) 27
(b) 25
(c) 28
(d) 30

Answer:

The given observations are 24, 25, 26, x + 2, x + 3, 30, 31, 34.

Median = 27.5

Here, n = 8

  
 

Hence, the correct option is (b).

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Question 16:

If the median of the data: 6, 7, x − 2, x, 17, 20, written in ascending order, is 16. Then x =

(a) 15
(b) 16
(c) 17
(d) 18

Answer:

The given observations arranged in ascending order are

Hence, the correct option is (c).

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Question 17:

The median of first 10 prime numbers is

(a) 11
(b) 12
(c) 13
(d) 14

Answer:

First 10 prime numbers are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29.

n = 10 (even)

  

Hence, the correct option is (b).

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Question 18:

If the mode of the data: 64, 60, 48, x, 43, 48, 43, 34 is 43, then x + 3 =

(a) 44
(b) 45
(c) 46
(d) 48

Answer:

Value 34 43 48 60 64 x
Frequency 1 2 2 1 1 1

It is given that the mode of the given date is 43. So, it is the value with the maximum frequency.

Now, this is possible only when x = 43. In this case, the frequency of the observation 43 would be 3.

Hence,

x + 3 = 46

Hence, the correct option is (c).

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Question 19:

If the mode of the data: 16, 15, 17, 16, 15, x, 19, 17, 14 is 15, then x =

(a) 15
(b) 16
(c) 17
(d) 19

Answer:

Value 14 15 16 17 19 x
Frequency 1 2 2 2 1 1

It is given that the mode of the data is 15. So, it is the observation with the maximum frequency.

This is possible only when x = 15. In this case, the frequency of 15 would be 3.

Hence, the correct answer is (a).

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Question 20:

The mean of 1, 3, 4, 5, 7, 4 is m. The numbers 3, 2, 2, 4, 3, 3, p have mean m − 1 and median q. Then, p + q =

(a) 4
(b) 5
(c) 6
(d) 7

Answer:



Consider the numbers 3, 2, 2, 4, 3, 3, p.

Mean = 3+2+3+4+3+3+p7

7×4-1=17+p21=17+pp=4

Arranging the numbers 3, 2, 2, 4, 3, 3, 4 in ascending order, we have

2, 2, 3, 3, 3, 4, 4


q = 3

So,

Hence, the correct option is (d).

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Question 21:

If the mean of frequency distribution is 8.1 and Σfixi = 132 + 5k, Σfi = 20, then k =

(a) 3
(b) 4
(c) 5
(d) 6

Answer:

Given:

Σfixi = 132 + 5k, Σfi = 20 and mean = 8.1.

Then,



Hence, the correct option is (d).

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Question 22:

If the mean of 6, 7, x, 8, y, 14 is 9, then

(a) x + y = 21
(b) x + y = 19
(c) xy = 19
(d) xy = 21

Answer:

The given observations are 6, 7, x, 8, y, 14.

Mean = 9          (Given)

6+7+x+8+y+146=935+x+y=54x+y=54-35=19

Hence, the correct option is (b).

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Question 23:

The mean of n observation is x. If the first observation is increased by 1, the second by 2, the third by 3, and so on, then the new mean is

(a) x+2n+1
(b) x+n+12
(c) x+n+1
(d) x-n+12

Answer:

Let x1, x2,x3,...,xn be the n observations.

Mean=x=x1+x2+...+xnn

x1+x2+x3+...+xn=nx

If the first item is increased by 1, the second by 2, the third by 3 and so on.

Then, the new observations are x1+1, x2+2,x3+3, ... ,xn+n.

New mean = x1+1+ x2+2+x3+3+...+xn+nn
                 =x1+x2+x3+...+xn+1+2+3+...+nn=nx+nn+12n=x+n+12

Hence, the correct answer is (c).

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Question 24:

If the mean of first n natural numbers is 5n9, then n =

(a) 5
(b) 4
(c) 9
(d) 10

Answer:

Given:
Mean of first n natural number =

1+2+3+...+nn=5n9nn+12n=5n9n+12=5n99n+9=10nn=9

Hence, the correct option is (c).



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Question 25:

The arithmetic mean and mode of a data are 24 and 12 respectively, then its median is

(a) 25
(b) 18
(c) 20
(d) 22

Answer:

Given: Mean = 24 and Mode = 12

We know that

Mode = 3Median − 2Mean

⇒ 12 = 3Median − 2 × 24

⇒ 3Median = 12 + 48 = 60

⇒ Median = 20

Hence, the correct option is (c).

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Question 26:

The mean of first n odd natural number is

(a) n+12
(b) n2
(c) n
(d) n2

Answer:

The first n odd natural numbers are 1, 3, 5, ... , (2n − 1).

∴ Mean of first n odd natural numbers

=1+3+5+...+2n-1n=n21+2n-1n                 Sn=n2a+l=2n2=n

Hence, the correct answer is (c).

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Question 27:

The mean of first n odd natural numbers is n281, then n =
(a) 9
(b) 81
(c) 27
(d) 18

Answer:

The first n odd natural numbers are 1, 3, 5, ... , (2n − 1).

∴ Mean of first n odd natural numbers

=1+3+5+...+2n-1n=n21+2n-1n                 Sn=n2a+l=2n2=n

Now,
Mean of first n odd natural numbers = n281                    (Given)
n=n281n=81

Hence, the correct option is (b).

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Question 28:

If the difference of mode and median of a data is 24, then the difference of median and mean is

(a) 12
(b) 24
(c) 8
(d) 36

Answer:

Given: Mode − Median = 24

We know that

Mode = 3Median − 2Mean

Now,

Mode − Median = 2(Median − Mean)

⇒ 24 = 2(Median − Mean)

⇒ Median − Mean = 12

Hence, the correct option is (a).

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Question 29:

If the arithmetic mean, 7, 8, x, 11, 14 is x, then x =

(a) 9
(b) 9.5
(c) 10
(d) 10.5

Answer:

The given observations are 7, 8, x, 11, 14.

Mean = x       (Given)

Now,

Mean=7+8+x+11+145x=40+x55x=40+x4x=40x=10 

Hence, the correct option is (c).

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Question 30:

If mode of a series exceeds its mean by 12, then mode exceeds the median by

(a) 4
(b) 8
(c) 6
(d) 10

Answer:

Given: Mode − Mean = 12

We know that

Mode = 3Median − 2Mean

∴ Mode − Mean = 3(Median − Mean)

⇒ 12 = 3(Median − Mean)

⇒ Median − Mean = 4       .....(1)

Again,

Mode = 3Median − 2Mean

⇒ 2Mode = 6Median − 4Mean

⇒ Mode − Mean + Mode = 6Median − 5Mean

⇒ 12 + (Mode − Median) = 5(Median − Mean)

⇒12 + (Mode − Median) = 20                              [Using (1)]

⇒ Mode − Median = 20 − 12 = 8

Hence, the correct option is (b).

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Question 31:

If the mean of first n natural number is 15, then n =

(a) 15
(b) 30
(c) 14
(d) 29

Answer:

Given:

Mean of first n natural numbers = 15

1+2+3+...+nn=15nn+12n=15n+12=15n+1=30n=29     

Hence, the correct option is (d).

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Question 32:

If the mean of observation x1, x2, ...., xn is x, then the mean of x1 + a, x2 + a, ....., xn + a is

(a) ax
(b) x-a
(c) x+a
(d) xa

Answer:

The mean of x1, x2, ..., xn is x.

x1+x2+x3+...+xnn=xx1+x2+x3+...+xn=nx

Mean of x1 + a, x2 + a, ... , xn + a

=x1+a+x2+a+x3+a+...+xn+an=x1+x2+x3+...+xn+a+a+a+...+an=nx+nan=x+a 

Hence, the correct option is (c).

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Question 33:

Mean of a certain number of observation is x. If each observation is divided by m(m ≠ 0) and increased by n, then the mean of new observation is

(a) xm+n
(b) xn+m
(c) x+nm
(d) x+mn

Answer:

Let y1, y2, y3,..., yk be k observations.

Mean of the observations = x

y1+y2+y3+...+ykk=xy1+y2+y3+...+yk=kx       .....1

If each observation is divided by m and increased by n, then the new observations are

y1m+n, y2m+n, y3m+n, ... , ykm+n

∴ Mean of new observations

=y1m+n+ y2m+n+...+ykm+nk=y1m+y2m+...+ykm+ n+n+...+nk=y1+y2+...+ykmk+nkk=kxmk+nkk=xm+n

Hence, the correct option is (a).

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Question 34:

If ui=xi-2510, Σfiui=20, Σfi=100, then x =

(a) 23
(b) 24
(c) 27
(d) 25

Answer:

Given:  ui=xi-2510, Σfiui=20 and Σfi=100

Now, = xi-2510

Therefore, h = 10 and A = 25

We know that

Hence, the correct option is (c).

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Question 35:

If 35 is removed from the data: 30, 34, 35, 36, 37, 38, 39, 40, then the median increased by

(a) 2
(b) 1.5
(c) 1
(d) 0.5

Answer:

The given data set is

If 35 is removed, then the new data set is 

30, 34, 36, 37, 38, 39, 40

n = 7 (odd)

Therefore,

Increase in median

Hence, the correct option is (d).

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Question 36:

 While computing mean of grouped data , we assume that the frequencies are 
(a) evenly distributed over all the classes.
(b) centred at the class marks of the classes .
(c) centred at the upper limit of the classes.
(d) centred at the lower limit of the classes.

Answer:

We know that while computing the mean of a grouped data, the frequencies are centered at the class marks of the classes.
Hence, the correct answer is option (b).

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Question 37:

In the formula  X¯ = a + h 1NΣfiui  , for finding the mean of grouped frequency distribution ui =
(a) xi + ah     (b)  hxi - a      (c) xi- ah     (d)  a -xih

Answer:


It is given that .
This is the formula to find mean of any data by step deviation method.

Here,
ui=xi-AhWhere xi are the mid values, A is assumed mean and h is class size.
Hence, the correct answer is option (c).



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Question 38:

For the following distribution :

Class:               0-5         5-10        10-15        15-20        20-25

Frequency:        10            15            12            20              9

the sum of the lower limits  of the median and modal class is 
(a)  15      (b)  25       (c)   30      (d)   35

Answer:

 

Class Frequency Cumulative Frequency
0–5 10 10
5–10 15 25
10–15 12 37
15–20 20 57
20–25 9 66
 Here, N = 66.
N2=33, which lies in the interval 10–15.
So, the lower limit of the median class is 10.
The highest frequency is 20, which lies in the interval 15–20.
Therefore, the lower limit of modal class is 15.
So, the required sum is 10 + 15 = 25.
Hence, the correct answer is option (b).

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Question 39:

 For the following distribution: 
   Below:                       10         20       30      40      50     60

Number of students:      3          12        27      57      75      80

the modal class is 

(a) 10-20        (b)  20-30       (c)  30-40        (d)    50-60

Answer:

 

Below Class Interval Cumulative Frequency Frequency
10 0–10 3 3
20 10–20 12 9
30 20–30 27 15
40 30–40 57 30
50 40–50 75 18
60 50–60 80 5
 
Here, N = 80.
N2=40, which lies in the interval 30–40.
Therefore, the modal class is 30–40.
Hence, the correct answer is option (c).

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Question 40:

Consider the following frequency distributions:
Class:              65-85          85-105        105-125    125-145     145-165    165-185   - 185-205

Frequency:      4                  5                    13              20              14              7                  4

The difference of the upper limit of the median class and the lower limit of the modal class is 
(a)  0     (b)    19       (c)   20        (d) 38  

Answer:

 

Class Frequency Cumulative frequency
65–85 4 4
85–105 5 9
105–125 13 22
125–145 20 42
145–165 14 56
165–185 7 63
185–205 4 67
 
Here, N = 67.
N2=33.5, which lies in the interval 125–145.
Therefore, the lower limit of the median class is 125.
The highest frequency is 20, which lies in the interval 125–145.
Therefore, the upper limit of modal class is 145.
So, the required difference is 145 − 125 = 20.
Hence, the correct answer is option (c).

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Question 41:

 In the formula X¯ = a+Σ fidiΣ fi , for finding the mean of grouped data di's  are derivations from a of
(a)  lower limits of classes        (b)  upper limits ofclasses     
(c)  mid-points of classes          (d) frequency of the class marks 

Answer:

The given formula represents the formula to find the mean by assumed mean method.
Here, dxi-a where xi is the ith observation and a is assumed mean. 
So, di's are the deviation from a of mid-points of the classes.
Hence, the correct answer is option (c).

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Question 42:

The abscissa of the point of intersection of less than type and of the more than types cumulative frequency curves of a grouped data gives its 
(a)  mean       (b)  median    (c) mode     (d)   all the three above

Answer:

The less than ogive and more than ogive when drawn on the same graph intersect at a point. From this point, if we draw a perpendicular on the x-axis, the point at which it cuts the x-axis gives us the median.
Thus, the abscissa of the point of intersection of less than type and of the more than type cumulative curves of a grouped data gives its median.
Hence, the correct answer is option (b). 

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Question 43:

Consider the following frequency distribution :
Class:               0-5               6-11               12-17               18-23                24-29

Frequency:       13                  10                 15                      8                     11

The upper limit of the median class is 
(a) 17         (b)   17.5       (c)   18           (d)    18.5

Answer:

The given classes in the table are non-continuous. So, we first make the classes continuous by adding 0.5 to the upper limit and subtracting 0.5 from the lower limit in each class. 

Class Frequency Cumulative
Frequency
0.5–5.5 13 13
5.5–11.5 10 23
11.5–17.5 15 38
17.5–23.5 8 46
23.5–29.5 11 57

Now, from the table we see that N = 57.
So, N2=572=28.5
28.5 lies in the class 11.5–17.5.
The upper limit of the interval 11.5–17.5 is 17.5. 
Hence, the correct answer is option (b).



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