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	Number of students
0 - 6	11
6 - 10	10
10 - 14	7
14 - 20	4
20 - 28	4
28 - 38	3
38 - 40	1

We will use assumed mean method to find the mean. Here, a is the assumed mean.

By formula,

Class mark = $\dfrac{\text{Upper limit + Lower limit}}{2}$

By formula,

Mean = $a + \dfrac{Σf$idi}{Σf_i}

Substituting values we get :

$\text{Mean } = 17 + \dfrac{-181}{40} \\[1em] = 17 - \dfrac{181}{40} \\[1em] = 17 - 4.525 \\[1em] = 12.475 ≈ 12.48$

Hence, mean number of days = 12.48