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Question
The following are the marks obtained by 70 boys in a class test:
| Marks | No. of boys |
| 30 – 40 | 10 |
| 40 – 50 | 12 |
| 50 – 60 | 14 |
| 60 – 70 | 12 |
| 70 – 80 | 9 |
| 80 – 90 | 7 |
| 90 – 100 | 6 |
Calculate the mean by:
Short-cut method
Solution
Short-cut method
|
Marks |
No. of boys |
Mid-value |
A = 65 |
fidi |
| 30 – 40 | 10 | 35 | –30 | –300 |
| 40 – 50 | 12 | 45 | –20 | –240 |
| 50 – 60 | 14 | 55 | –10 | –140 |
| 60 – 70 | 12 | A = 65 | 0 | 0 |
| 70 – 80 | 9 | 75 | 10 | 90 |
| 80 – 90 | 7 | 85 | 20 | 140 |
| 90 – 100 | 6 | 95 | 30 | 180 |
| Total | 70 | –270 |
`barx = A + (sumf_i d_i)/(sumf_i)`
= `65 + ((-270)/70)`
= 65 – 3.86
= 61.14
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