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Question
Find the mean of each of the following frequency distributions
| Class interval | 0 - 8 | 8 - 16 | 16 - 24 | 24 - 32 | 32 - 40 |
| Frequency | 6 | 7 | 10 | 8 | 9 |
Solution
Let the assumed mean A = 20
| Class interval |
Mid-value(x1) | d1 = x1 - 20 | `"u"_1=(x_1-20)/8` | f1 | f1u1 |
| 0 - 8 | 4 | -16 | -2 | 6 | -12 |
| 8 - 16 | 12 | -8 | -1 | 7 | -7 |
| 16 - 24 | 20 | 0 | 0 | 10 | 0 |
| 24 - 32 | 28 | 8 | 1 | 8 | 8 |
| 32 - 40 | 36 | 16 | 2 | 9 | 18 |
| N = 40 | `sumf_1"u"_1=7` |
We have
A = 20 h = 8
Mean `=A+hxx(sumf_1"U"_1)/N`
`=20+8xx7/40`
`=20+56/40`
= 20 + 1.4
= 21.4
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