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Question
Find the mean of each of the following frequency distributions
| Class interval | 0 - 6 | 6 - 12 | 12 - 18 | 18 - 24 | 24 - 30 |
| Frequency | 7 | 5 | 10 | 12 | 6 |
Solution
Let the assume mean A = 15
| Class interval |
Mid-value(x1) | d1 = x1 - 15 | `"u"_1=(x_1-15)/6` | Frequency(f1) | f1u1 |
| 0 - 6 | 3 | -12 | -2 | 7 | -14 |
| 6 - 12 | 9 | -6 | -1 | 5 | -5 |
| 12 - 18 | 15 | 0 | 0 | 10 | 0 |
| 18 - 24 | 21 | 6 | 1 | 12 | 12 |
| 24 - 30 | 27 | 12 | 2 | 6 | 12 |
| N = 40 | `sumf_1"u"_1=5` |
We have
A = 15 h = 6
Mean `=A+hxx(sumf_1"u"_1)/N`
`=15+6xx5/40`
`=15+30/40`
= 15 + 0.75
= 15.75
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