The exam results of 250 students are listed below. Determine the mean.

Class interval	0-9	10-19	20-29	30-39	40-49
Frequency	0	2	6	24	36
Class interval	50-59	60-69	70-79	80-89	90-99
Frequency	47	55	40	27	13

The sum of the values of all the observations $=f_1{x}_1+f_2{x}_2+\dots +f_n{x}_n$, and the number of observations $=f_1+f_2+\dots +f_n$.

So, the mean $\overline{x}$ of the data is given by

$\overline{x}=\frac{f_1{x}_1+f_2{x}_2+\cdots +f_n{x}_n}{f_1+f_2+\cdots +f_n}$

$\text{ Mean }=\frac{\text{ Total }(\text{ midvalue }\times \text{ frequency })}{\text{ Totalfrequency }}$

$\text{ Mean }=\frac{\text{ Total }(\text{ midvalue }\times \text{ frequency })}{\text{ Totalfrequenct }}=\frac{15205}{250}=60.82$