9.  Given the following data on monthly wages of 1000 workers, frequency of two class interval are missing.  Locate these if, Median of the series is 50.
Wages (in Rs) 20-30 30-40 40-50 50-60 60-70 70-80
No. of workers 60 60 ? 200 ? 285

10.  Calculate mode in the following distribution using grouping method:-
Marks 40-49 50-59 60-69 70-79 80-89 90-99
f 12 3 24 20 12 2

Dear Student,

9)
Wages   frequency cumulative frequency
20-30 60 60
30-40 60 120
40-50 f1 120+ f1
50-60 200  320 + f1
60-70 f2 320 + f1 +f2
70-80 285 605 + f1 +f2
Total 1000 1000

605 + f1 + f2 = 1000
f1 + f2 = 395 --------------------- (i)

As median is 56 median class is 50-60

Median = l + n/2 - cf / f * i
56 = 50 + 1000/2 - ( 120 + f1 ) / 200 * 10
56 = 50 + 500 - 120 - f1 / 20
56 = 1000 + 380 - f1 / 20
56 * 20 = 1380 - f1
1120  = 1380 - f1
f1 = 260

substituting value in (i)
f1 + f2 = 395
260 + f2 = 395
f2 = 135

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