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 − 10	10 − 14	14 − 20	20 − 28	28 − 38	38 − 40
Number of students	11	10	7	4	4	3	1

Answer 1

To find the class mark of each interval, the following relation is used.

Taking 17 as assumed mean (a), d_i and f_id_i are calculated as follows.

Number of days	Number of students fi	xi	di = xi − 17	fidi
0 − 6	11	3	− 14	− 154
6 − 10	10	8	− 9	− 90
10 − 14	7	12	− 5	− 35
14 − 20	4	17	0	0
20 − 28	4	24	7	28
28 − 38	3	33	16	48
38 − 40	1	39	22	22
Total	40			− 181

From the table, we obtain

Therefore, the mean number of days is 12.48 days for which a student was absent.