Class interval: | 0-8 | 8-16 | 16-24 | 24-32 | 32-40 |
Frequency: | 5 | 9 | 10 | 8 | 8 |
Let the assumed mean (A) = 20
Class interval | Mid value (xi) | di = xi - 20 | ui = | Frequency (fi) | fiui � |
0 – 8 | 4 | -16 | -2 | 5 | -10 |
8 – 16 | 12 | -8 | -1 | 9 | -9 |
16 – 24 | 20 | 0 | 0 | 10 | 0 |
24 – 32 | 28 | 8 | 1 | 8 | 8 |
32 – 40 | 36 | 16 | 2 | 8 | 16 |
N = 40 | ∑fiui = 5 |
We have, A = 20
h = 8
Mean = A + h * 
= 20 + 8 * 
= 20 + 1 = 21
10