Question

Find the mean of the following frequency distribution : 

Class	50-60	60-70	70-80	80-90	90-100
Frequency	8	6	12	11	13

Answer 1

Class Interval	Xi	fi	fiXi
50-60	55	8	440
60-70	65	6	390
70-80	75	12	900
80-90	85	11	935
90-100	95	13	1235
Total		50	3900

${\displaystyle \overline{x}= \frac{\Sigma f_i{X}_i}{\Sigma \text{f}}}$

${\displaystyle \overline{x}=\frac{3900}{50}}$

${\displaystyle \overline{x}=78}$

${\displaystyle \therefore }$ Mean = 78