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Question
Using step-deviation method, find mean for the following frequency distribution:
| Class | 0 – 15 | 15 – 30 | 30 – 45 | 45 – 60 | 60 – 75 | 75 – 90 |
| Frequency | 3 | 4 | 7 | 6 | 8 | 2 |
Solution
| Class | x | u = d/i | f | fu |
| 0 – 15 | 7.5 | –3 | 3 | –9 |
| 15 – 30 | 22.5 | –2 | 4 | –8 |
| 30 – 45 | 37.5 | –1 | 7 | –7 |
| 45 – 60 | 52.5 | 0 | 6 | 0 |
| 60 – 75 | 67.5 | 1 | 8 | 8 |
| 75 – 90 | 82.5 | 2 | 2 | 4 |
| 30 | –12 |
Mean = `A + (sumfu)/(sumf) xx i`
= `52.5 + (-12)/30 xx 15`
= 52.5 – 6
= 46.50
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