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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 :

Class interval Frequency \( (f_i) \) Mid-point \( (x_i) \) \( f_i x_i \)
0-6 11 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
\( \sum f_i \ = \ 40 \) \( \sum f_i x_i \ = \ 499 \)

The mean formula is,

\( \overline{x} \ = \ \frac{ \sum \ f_i x_i}{ \sum f_i} \)

\( = \ \frac{499}{40} \)

\(= \ 12.48 \) days

\(\therefore \) The mean number of days a student was absent = 12.48.

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