Question

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 1

$No.ofdays$	$Classmark$ $x_i$	$No.ofstudents$ $f_i$	$f_i{x}_i$
$0-6$	$3$	$11$	$33$
$6-10$	$8$	$10$	$80$
$10-14$	$12$	$7$	$84$
$14-20$	$17$	$4$	$68$
$20-28$	$24$	$4$	$96$
$28-38$	$33$	$3$	$99$
$38-40$	$39$	$1$	$39$
		$\sum f_i=40$	$\sum f_i{x}_i=499$

$Mean\left(\overline{x}\right)=\frac{\sum f_i{x}_i}{\sum f_i}$

$=\frac{499}{40}$

$=12.5$