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.

Answer 1

Let be assumed mean (A) = 3

No. of calls (xi)	No. of intervals (fi)	ui = xi − A (A = 3)	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