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Question
Find the mean of each of the following frequency distributions: (5 - 14)
| Class interval | 0 - 6 | 6 - 12 | 12 - 18 | 18 - 24 | 24 - 30 |
| Frequency | 6 | 8 | 10 | 9 | 7 |
Solution
Let a assume mean be 15
| Class interval | Mid-value(x1) | d1 = x1 - 15 | `"u"_1=(x_1-15)/6` | f1 | f1u1 |
| 0 - 6 | 3 | -12 | -2 | 6 | -12 |
| 6 - 12 | 9 | -6 | -1 | 2 | -8 |
| 12 - 18 | 15 | 0 | 0 | 10 | 0 |
| 18 - 24 | 21 | 6 | 1 | 9 | 9 |
| 24 - 30 | 27 | 12 | 2 | 7 | 14 |
| N = 40 | `sumf_1"u"_1=3` |
A = 15, h = 5
Mean `=A = hxx(sumf_1"u"_1)/N`
`=15+6xx3/40`
`= 15 + 18/40`
= 15 + 0.45
= 15.45
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