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Question
Find the mean of each of the following frequency distributions
| Class interval | 0 - 10 | 10 - 20 | 20 - 30 | 30 - 40 | 40 - 50 |
| Frequency | 9 | 12 | 15 | 10 | 14 |
Solution
Let the assumed mean A = 25
| Class interval | Mid value(x1) | d1 = x1 - 25 | `"u"_1=(x_1-25)/10` | f1 | f1u1 |
| 0 -10 | 5 | -20 | -2 | 9 | -18 |
| 10 - 20 | 15 | -10 | -1 | 12 | -12 |
| 20 - 30 | 25 | 0 | 0 | 15 | 0 |
| 30 - 40 | 35 | 10 | 1 | 10 | 10 |
| 40 - 50 | 45 | 20 | 2 | 14 | 28 |
| N = 60 | `sumf_1"u"_1=8` |
We have
A = 25, h = 10
Mean `=A+hxx(sumf_1"u"_1)/N`
`=25+10xx8/60`
`=25+80/60`
= 25 + 1.333
= 26.333
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