Chapter 15.8, Problem 12E

The frequency of repair for the trucks owned by a truck­ing firm over a 5­year period has been tabulated. The results are shown in the following frequency distribution. Find the mean number of repairs over the 5­year period.

Time repaired	Frequency
1.5-2.5	22
2.5-3.5	53
3.5-4.5	72
4.5-5.5	108
5.5-6.5	102
6.5-7.5	120
7.5-8.5	146
8.5-9.5	135
9.5-10.5	98
10.5-11.5	98
11.5-12.5	84
12.5-13.5	12
13.5-14.4	8