Question

A class teacher has the following absentee record of 40 students of a class for the whole term. Find the mean number of days a student was absent.

Number of days:	0-6	6-12	12-18	18-24	24-30	30-36	36-42
Number of students:	10	11	7	4	4	3	1

Answer 1

We will do it by a direct method

Using: mean`(∑ "f"_"i""x"_"i")/(∑ "f"_"i")`

Number of days	Number of students  (fi)	Classmark  (xi)	fixi
0-6	10	`(0+6)/2 = 3`	30
6-12	11	`(6+12)/2 = 9`	99
12-18	7	`(12+18)/2 =15`	105
18-24	4	`(18+24)/2 = 21`	84
24-30	4	`(24+30)/2 =27`	108
30-36	3	`(30+46)/2 =33`	99
36-42	1	`(36+42)/2 = 39`	39
	∑ fi = 40		∑ fixi =564

substituting the values in the formula

mean = `564/40 = 14.1`