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प्रश्न
Find mean of the following table.
| Difference in ages (in years) |
No. of couples (fi) |
| 0 – 2 | 1 |
| 2 – 4 | 2 |
| 4 – 6 | 8 |
| 6 – 8 | 5 |
| 8 – 10 | 3 |
| 10 – 12 | 1 |
बेरीज
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उत्तर
1. Calculation table
First, find the class mark (midpoint xi) for each interval using the formula:
Class Mark (xi) = `("Lower Limit" + "Upper Limit")/2`
| Difference in ages (in years) |
No. of couples (fi) |
Class Mark (xi) |
fi × xi |
| 0 – 2 | 1 | 1 | 1 × 1 = 1 |
| 2 – 4 | 2 | 3 | 2 × 3 = 6 |
| 4 – 6 | 8 | 5 | 8 × 5 = 40 |
| 6 – 8 | 5 | 7 | 5 × 7 = 35 |
| 8 – 10 | 3 | 9 | 3 × 9 = 27 |
| 10 – 12 | 1 | 11 | 1 × 11 = 11 |
| Total | Σfi = 20 | Σfixi = 120 |
2. Formula and Final Steps
Using the direct method formula for calculating the mean:
Mean `(barx) = (sumf_ix_i)/(sumf_i)`
`barx = 120/20`
`barx` = 6
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