RD Sharma Solutions for Class 10 Math Chapter 7 Statistics are provided here with simple step-by-step explanations. These solutions for Statistics are extremely popular among class 10 students for Math Statistics Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the RD Sharma Book of class 10 Math Chapter 7 are provided here for you for free. You will also love the ad-free experience on Meritnation’s RD Sharma Solutions. All RD Sharma Solutions for class 10 Math are prepared by experts and are 100% accurate.
Page No 7.13:
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 7.13:
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 7.13:
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 7.13:
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 7.13:
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 7.13:
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 7.13:
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 7.13:
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 7.14:
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 7.22:
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 7.22:
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 7.22:
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 7.22:
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 | No. of Women : | |||
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 |
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 7.22:
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 7.22:
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 7.23:
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 7.23:
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 7.23:
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 7.23:
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 7.23:
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 7.23:
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 7.23:
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 7.23:
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) | |||
24.529.5 | 27 | 14 | −15 | −3 | −42 |
29.534.5 | 32 | 22 | −10 | −2 | −44 |
34.539.5 | 37 | 16 | −5 | −1 | −16 |
39.544.5 | A = 42 | 6 | 0 | 0 | 0 |
44.549.5 | 47 | 5 | 5 | 1 | 5 |
49.554.5 | 52 | 3 | 10 | 2 | 6 |
54.559.5 | 57 | 4 | 15 | 3 | 12 |
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 7.23:
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) | Frequency(fi) | ||
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 = |
Let the assumed mean be A = 12.5.
We know that mean,
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 7.23:
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 7.23:
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,
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 7.23:
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 | 8 |
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 7.24:
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
Page No 7.24:
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 7.24:
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) | |||
49.552.5 | 51 | 15 | −6 | −2 | −30 |
52.555.5 | 54 | 110 | −3 | −1 | −110 |
55.558.5 | 57 | 135 | 0 | 0 | 0 |
58.561.5 | 60 | 115 | 3 | 1 | 115 |
61.564.5 | 63 | 25 | 6 | 2 | 50 |
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 7.24:
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 | 25 | − 7 |
Now,
Therefore, mean daily expenditure on food is Rs 211.
Page No 7.24:
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
Hence, the mean concentration of SO2in the air is 0.099 ppm.
Page No 7.24:
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 7.24:
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 7.24:
Question 19:
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 7.34:
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 7.34:
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 7.34:
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,
Hence, the median is 99.35.
Page No 7.34:
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 7.34:
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 7.34:
Question 6:
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 7.34:
Question 7:
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 7.34:
Question 8:
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 7.34:
Question 9:
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 7.35:
Question 10:
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
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 7.35:
Question 11:
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 7.35:
Question 12:
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 7.35:
Question 13:
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 7.35:
Question 14:
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 7.35:
Question 15:
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 7.36:
Question 16:
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 7.36:
Question 17:
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 | 5880 |
Mean length of the leaf =
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
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 7.36:
Question 18:
The following table gives the distribution of the life time of 400 neon lamps:
Life 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 7.44:
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 7.44:
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 7.44:
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 7.45:
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 7.45:
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 7.45:
Question 9:
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 7.45:
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 7.45:
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 =
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 7.45:
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 7.45:
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. (fi) |
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.
Mean of the data =
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 7.46:
Question 11:
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,
Thus, the mode of the data (or runs scored) is 4608.7.
Page No 7.46:
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,
Thus, the mode of the data is 44.7.
Page No 7.46:
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,
∴ Median
= 137
Thus, the median of the monthly consumption of electricity is 137 units.
Page No 7.46:
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 7.46:
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 7.46:
Question 16:
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 |
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 7.46:
Question 17:
The following table 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 |
Find the mean, mode and median of the above data.
Answer:
Consider the following table.
Daily income (in Rs.) | Number of workers (fi) | xi | fi xi | C.f. | |
100−120 | 12 | 110 | 1320 | 12 | |
120−140 | 14 | 130 | 1820 | 26 | |
140−160 | 8 | 150 | 1200 | 34 | |
160−180 | 6 | 170 | 1020 | 40 | |
180−200 | 10 | 190 | 1900 | 50 | |
Here, the maximum frequency is 14 so the modal class is 120−140.
Therefore,
Thus, the mean daily income of the workers is Rs 145.20.
Thus, the median of the daily income of the workers is Rs 138.57.
Thus, the mode of the daily income of the workers is Rs 125.
Page No 7.5:
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 7.5:
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 7.5:
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 7.5:
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 7.5:
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 7.5:
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 7.5:
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,
Hence, p
Page No 7.5:
Question 8:
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,
By using cross multiplication method,
Hence, p
Page No 7.6:
Question 9:
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 7.6:
Question 10:
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,
By using cross multiplication method,
Hence, the number of candidates that appeared from school III is 124.
Page No 7.6:
Question 11:
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,
Hence, the mean number of heads per toss is 2.47.
Page No 7.6:
Question 12:
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 7.6:
Question 13:
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 7.6:
Question 14:
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 7.6:
Question 15:
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 7.61:
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 7.61:
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 7.62:
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 7.62:
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 7.62:
Question 5:
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 7.62:
Question 6:
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 |
Suitable |
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 7.62:
Question 7:
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 7.62:
Question 8:
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 7.63:
Question 9:
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 7.63:
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 7.63:
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 7.63:
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 7.64:
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 7.64:
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 7.64:
Question 6:
Which measure of central tendency can be determine graphically?
Answer:
Median can be determined graphically.
Page No 7.64:
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.
Page No 7.64:
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
Page No 7.64:
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
The cumulative frequency just greater than 50 is 60.
So, the median class is 40−50.
Page No 7.64:
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)
Mode − Mean = k (Median − Mean) .....(2)
From (1) and (2), we get
k = 3
Page No 7.64:
Question 11:
Find the class marks of classes 10−25 and 35−55.
Answer:
Class mark of 10−25
Class mark of 35−55
Page No 7.64:
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.Page No 7.65:
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).
Page No 7.65:
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).
Page No 7.65:
Question 3:
The arithmetic mean of 1, 2, 3, ... , n is
(a)
(b)
(c)
(d)
Answer:
Arithmetic mean of 1, 2, 3, ... , n
Hence, the correct option is (a).
Page No 7.65:
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).
Page No 7.65:
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).
Page No 7.65:
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).
Page No 7.65:
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).
Page No 7.65:
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).
Page No 7.65:
Question 9:
The mean of n observation is . If the first item is increased by 1, second by 2 and so on, then the new mean is
(a)
(b)
(c)
(d) None of these
Answer:
Let be the n observations.
Mean
If the first item is increased by 1, second by 2 and so on.
Then, the new observations are .
New mean =
Hence, the correct answer is (c).
Page No 7.65:
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).
Page No 7.65:
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).
Page No 7.65:
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).
Page No 7.66:
Question 13:
The mean of a discrete frequency distribution xi / fi, i = 1, 2, ......, n is given by
(a)
(b)
(c)
(d)
Answer:
The mean of discrete frequency distribution is
Hence, the correct option is (a).
Page No 7.66:
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.
Now,
Hence, the correct option is (d).
Page No 7.66:
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).
Page No 7.66:
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).
Page No 7.66:
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).
Page No 7.66:
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).
Page No 7.66:
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).
Page No 7.66:
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 =
2, 2, 3, 3, 3, 4, 4
∴ q = 3
So,
Hence, the correct option is (d).
Page No 7.66:
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).
Page No 7.66:
Question 22:
If the mean of 6, 7, x, 8, y, 14 is 9, then
(a) x + y = 21
(b) x + y = 19
(c) x − y = 19
(d) x − y = 21
Answer:
The given observations are 6, 7, x, 8, y, 14.
Mean = 9 (Given)
Hence, the correct option is (b).
Page No 7.66:
Question 23:
The mean of n observation is . 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)
(b)
(c)
(d)
Answer:
Let be the n observations.
Mean
If the first item is increased by 1, the second by 2, the third by 3 and so on.
Then, the new observations are .
New mean =
Hence, the correct answer is (c).
Page No 7.66:
Question 24:
If the mean of first n natural numbers is , then n =
(a) 5
(b) 4
(c) 9
(d) 10
Answer:
Given:
Mean of first n natural number =
Hence, the correct option is (c).
Page No 7.67:
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).
Page No 7.67:
Question 26:
The mean of first n odd natural number is
(a)
(b)
(c) n
(d) n2
Answer:
The first n odd natural numbers are 1, 3, 5, ... , (2n − 1).
∴ Mean of first n odd natural numbers
Hence, the correct answer is (c).
Page No 7.67:
Question 27:
The mean of first n odd natural numbers is , 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
Now,
Mean of first n odd natural numbers = (Given)
Hence, the correct option is (b).
Page No 7.67:
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).
Page No 7.67:
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,
Hence, the correct option is (c).
Page No 7.67:
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).
Page No 7.67:
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
Hence, the correct option is (d).
Page No 7.67:
Question 32:
If the mean of observation , then the mean of x1 + a, x2 + a, ....., xn + a is
(a)
(b)
(c)
(d)
Answer:
The mean of .
Mean of x1 + a, x2 + a, ... , xn + a
Hence, the correct option is (c).
Page No 7.67:
Question 33:
Mean of a certain number of observation is . If each observation is divided by m(m ≠ 0) and increased by n, then the mean of new observation is
(a)
(b)
(c)
(d)
Answer:
Let be k observations.
Mean of the observations =
If each observation is divided by m and increased by n, then the new observations are
∴ Mean of new observations
Hence, the correct option is (a).
Page No 7.67:
Question 34:
If =
(a) 23
(b) 24
(c) 27
(d) 25
Answer:
Given:
Now, =
Therefore, h = 10 and A = 25
We know that
Hence, the correct option is (c).
Page No 7.67:
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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