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.
Let the assumed mean (A) = 3
Number of calls (xi) | Number of intervals (fi �) | ui = xi – A = xi - 3 | fiui |
0 | 15 | -3 | -45 |
1 | 24 | -2 | -48 |
2 | 29 | -1 | -29 |
3 | 46 | 0 | 0 |
4 | 54 | 1 | 54 |
5 | 43 | 2 | 86 |
6 | 39 | 3 | 117 |
N = 250 | ∑fiui = 135 |
Mean number of calls = A +
= 3 + =
= 3.54