Class interval: | 50-70 | 70-90 | 90-110 | 110-130 | 130-150 | 150-170 |
Frequency: | 18 | 12 | 13 | 27 | 8 | 22 |
Let the assumed mean (A) be 100.
Class interval | Mid value (xi) | di = xi - 100 | ui = | fi | fiui |
50 – 70 | 60 | -40 | -2 | 18 | -36 |
70 – 90 | 80 | -20 | -1 | 12 | -12 |
90 – 110 | 100 | 0 | 0 | 13 | 0 |
110 – 130 | 120 | 20 | 1 | 27 | 27 |
130 – 150 | 140 | 40 | 2 | 8 | 16 |
150 – 170 | 160 | 60 | 3 | 22 | 66 |
N = 100 | ∑fiui = 61 |
A = 100, h = 20
Mean = A + h * 
= 100 + 20 * 
= 100 + 12.2
= 112.2
6