# A class teacher has the following absentee record of 40 students of a class for the whole term. Number of days: 0 - 6, 6 - 10, 10 -14

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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

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We may calculate class marks (xi) for each interval by using the relation

xi $=\frac{Upper\,class\,limit+lower\,class\,limit}{2}$

Now taking assumed mean (A) = 16

 Number of days Number of students (fi) xi di = xi - 16 fidi 0 - 6 11 3 -13 -143 6 - 10 10 5 -8 -80 10 - 14 7 12 -4 -28 14 - 20 4 16 0 0 20 - 28 4 24 8 32 28 - 38 3 33 17 51 38 - 40 1 39 23 23 N = 40 $\sum$fidi = -145

Mean (x̅) = A + $\frac{\sum fidi}{N}$

$=16+\frac{-145}{40}$

$=16 - 3.62=12.38$

So,

mean number of days is 12.38 days for which students were absent.