Calculate the mean of the following data, using direct method:
Class | 25 - 35 | 35 - 45 | 45 - 55 | 55 - 65 | 65 - 75 |
Frequency | 6 | 10 | 8 | 12 | 4 |
For equal class intervals, we will solve by finding mid points of these classes using direct method.
CLASS | MID - POINT(xi) | FREQUENCY(fi) | fixi |
25 - 35 | 30 | 6 | 180 |
35 - 45 | 40 | 10 | 400 |
45 - 55 | 50 | 8 | 400 |
55 - 65 | 60 | 12 | 720 |
65 - 75 | 70 | 4 | 280 |
TOTAL | 40 | 1980 |
We have got
Σfi = 40 & Σfixi = 1980
∵ mean is given by
⇒ 
⇒ 
Thus, mean is 49.5
5