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Question
The number of telephone calls received at an exchange per interval for 250 successive one minute intervals are given in the following frequency table:
| No. of calls(x) | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
| No. of intervals (f) | 15 | 24 | 29 | 46 | 54 | 43 | 39 |
Compute the mean number of calls per interval.
Solution
Let be assumed mean (A) = 3
|
No. of calls |
No. of intervals |
ui = xi − A |
fiui |
| 0 | 15 | −3 | −45 |
| 1 | 24 | −2 | −47 |
| 2 | 29 | −1 | −39 |
| 3 | 46 | 0 | 0 |
| 4 | 54 | 1 | 54 |
| 5 | 43 | 2 | 86 |
| 6 | 39 | 3 | 47 |
| N = 250 | `sumf_ix_i=135` |
Mean number of cells `=A+(sumf_ix_i)/N`
= `3+135/250`
= `(750 + 135)/250`
= `885/250`
= 3.54
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