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.

`x_i  = ("Upper class limit + Lower class limit")/2`

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

Number of days	Number of students fi	Mid value(xi)	di = xi − 17	fixi
0 − 6	11	3	− 14	33
6 − 10	10	8	−9	80
10 − 14	7	12	−5	84
14 − 20	4	17	0	68
20 − 28	4	24	7	96
28 − 38	3	33	16	99
38 − 40	1	39	22	39
Total	40			499

From the table, we obtain

`sumf_i = 40`

`sumf_ix_i = 499`

`"Mean " barx = ((sumf_ix_i)/(N))`

`= (499/40)`

=12.475

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