Question

8. 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.By step deviation method.
0-6
6 - 10 10 - 14 14 - 2020-28 28 - 38 38 - 40
Number of
days
Number of
students
11
10
7
4
4
3
1​

Answer 1

Since the class interval is not same, we need to find the mean of the group of data by direct method.  

The mean of data from direct method = ∑(f * x)/∑( f)

f – Frequency

x – Class average = (lower bound + upper bound) / 2  

Let us represent all data in the table below as

Number  number of      Class fx

of days students (f) average (x)

0 – 6     11   (0+6)/2 = 3 33

6 – 10     10   8           80

10 – 14       7   12           84

14 – 20     4   17           68

20 – 28     4   24             96

28 – 38      3   33           99

38 – 40      1     39           39

∑(fx) = 499

∑(f) = 40

Mean = 499/40 = 12.48