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.
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Solution
Let be assumed mean (A) = 3
|
No. of calls (x1) |
No. of intervals (f1) |
u1 = x1 - A (A = 3) |
f1u1 |
| 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_1u_1=135` |
Mean number of cells `=A+(sumf_1u_1)/N`
`=3+135/250`
`=(750 + 135)/250`
`=885/250`
= 3.54
Concept: Mean of Grouped Data
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