9. If the mean of the distribution is 57.6 and the sum of its observations is 50, find the missing
frequencies f1
and f2
C.I-
0-20 20-40 40-60 60-80 80-100 100-120
Fi
7 f1 12 f2 8 5
We have the following data
Class | Frequency fi | Mid-values xi | f ixi | |
0-20 | 7 | 10 | 70 | |
20-40 | f 1 | 30 | 30f 1 | |
40-60 | 12 | 50 | 600 | |
60-80 | f 2 | 70 | 70f 2 | |
80-100 | 8 | 90 | 720 | |
100-120 | 5 | 110 | 550 |
Since,
Again,
Multiply equation 1 by 3 and subtract it from equation 2 to get,