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.

Question :

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

Solution :

Here, the class size varies, and \(x_i\)’s are small,

Number of days	Mid-Value (\(x_i\))	Number Students (\(f_i\))	\(f_iu_i\)
0 – 6	3	11	33
6 – 10	8	10	80
10 – 14	12	7	84
14 – 20	17	4	68
20 – 28	24	4	96
28 – 30	33	3	99
38 – 40	39	1	39
Total		40	499

Let us apply the direct method here :

So, Mean = \(\sum f_iu_i\over \sum f_i\) = \(499\over 40\) = 12.475

Hence, mean = 12.48 days