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प्रश्न
Find the mean of each of the following frequency distributions
| Class interval | 10 - 30 | 30 - 50 | 50 - 70 | 70 - 90 | 90 - 110 | 110 - 130 |
| Frequency | 5 | 8 | 12 | 20 | 3 | 2 |
उत्तर
Let the assume mean A = 60
| Class interval | Mid value(x1) | d1 = x1 - 60 | `"u"_1=(x_1-60)/20` | f1 | f1u1 |
| 10 - 30 | 20 | -40 | -2 | 5 | -10 |
| 30 - 50 | 40 | -20 | -1 | 8 | -8 |
| 50 - 70 | 60 | 0 | 0 | 12 | 0 |
| 70 - 90 | 80 | 20 | 1 | 20 | 20 |
| 90 -110 | 100 | 40 | 2 | 3 | 6 |
| 110 - 130 | 120 | 60 | 3 | 2 | 6 |
| N = 50 | `sumf_1"u"_1=14` |
We have
A = 60, h = 20
Mean `=A+hxx(sumf_1"u"_1)/N`
`=60+20xx14/50`
`=60+280/50`
= 60 + 5.6
= 65.6
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