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Question
Compute the mean deviation about mean from the following data:
| Class Interval: | 0 - 5 | 5 - 10 | 10 - 15 | 15 - 20 | 20 - 25 |
| Frequency (f) | 3 | 5 | 12 | 6 | 4 |
Solution
| C.I. | X | f | fX | |D| = `|"X" - bar"X"|` = |X − 13| |
f|D| |
| 0 - 5 | 2.5 | 3 | 7.5 | 10.5 | 31.5 |
| 5 - 10 | 7.5 | 5 | 37.5 | 5.5 | 27.5 |
| 10 - 15 | 12.5 | 12 | 150.0 | 0.5 | 6.0 |
| 15 - 20 | 17.5 | 6 | 105.0 | 4.5 | 27.0 |
| 20 - 25 | 22.5 | 4 | 90.0 | 9.5 | 38 |
| N = ∑f = 30 | ∑fX = 390 | ∑f|D| = 130 |
Mean = `bar"X" = 390/30` = 13
Mean deviation about Mean = `(sum"f" |"D"|)/"N" = 130/30` = 4.33
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