Find the mean of the following data, using the Assumed - mean method:
Class | 0 - 20 | 20 - 40 | 40 - 60 | 60 - 80 | 80 - 100 | 100 - 120 |
Frequency | 20 | 35 | 52 | 44 | 38 | 31 |
We will find the mean of the data using Assumed - mean method, where A = Assumed mean.
CLASS | MID - POINT(xi) | FREQUENCY(fi) | DEVIATION(di) di = xi – 50 | fidi |
0 - 20 | 10 | 20 | - 40 | - 800 |
20 - 40 | 30 | 35 | - 20 | - 700 |
40 - 60 | 50 = A | 52 | 0 | 0 |
60 - 80 | 70 | 44 | 20 | 880 |
80 - 100 | 90 | 38 | 40 | 1520 |
100 - 120 | 110 | 31 | 60 | 1860 |
TOTAL | 220 | 2760 |
We have got
A = 50, Σfi = 220 & Σfidi = 2760
∵ mean is given by
⇒ 
⇒ 
Thus, mean is 62.55.
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