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प्रश्न
If the mean of the following observations is 54, find the value of p.
| Class | 0 – 20 | 20 – 40 | 40 – 60 | 60 – 80 | 80 – 100 |
| Frequency | 7 | p | 10 | 9 | 13 |
उत्तर
| Class | Frequency (f) | Mid value (x) | fx |
| 0 – 20 | 7 | 10 | 70 |
| 20 – 40 | p | 30 | 30p |
| 40 – 60 | 10 | 50 | 500 |
| 60 – 80 | 9 | 70 | 630 |
| 80 – 100 | 13 | 90 | 1170 |
| Total | 39 + p | 2370 + 30p |
`barx = (sumfx)/(sumf) = (2370 + 30p)/(39 + p)` ...(i)
Here mean = 54 ...(ii)
From (i) and (ii)
`(2370 + 30p)/(39 + p) = 54`
`=>` 2370 + 30p = 2106 + 54p
`=>` 54p – 30p = 2370 – 2106
`=> p = 264/24 = 11`
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