Question

Calculate the mean of the scores of $20$ students in a mathematics test : Marks $10-20,20-30,30-40,40-50,50-60$ . Number of students $2,4,7,6,1$

Answer 1

Let us first determine the class mark $x_i$ of each class and then proceed as follows

Class	Class Marks (xi)	Frequency (fi)	$fixi$
$10-20$	$15$	$2$	$30$
$20-30$	$25$	$4$	$100$
$30-40$	$35$	$7$	$245$
$40-50$	$45$	$6$	$270$
$50-60$	$55$	$1$	$55$
$\Sigma fi=20$	$\Sigma fixi=700$

Mean $\overline{x}=\frac{{\displaystyle \sum _{}^{}}{f}_i{x}_i}{{\displaystyle \sum _{}^{}}{f}_i}$

$$\begin{gathered} =\frac{700}{20} \\ =35 \end{gathered}$$

Therefore, mean of scores of $20$students in mathematics test $35$.