What is the solution of question 25.

Dear Student,

Consider the table below: 
 

Classes	Xi	Frequencies Fi	FiXi	Xi2	FiX​i2
30-40	35	3	105	1225	3675
40-50	45	7	315	2025	14175
50-60	55	12	660	3025	36300
60-70	65	15	975	4225	63375
70-80	75	8	600	5625	45000
80-90	85	3	255	7225	21675
90-100	95	2	190	9025	18050
		$\sum F_i=50$	$\sum F_i{X}_i=3100$		$\sum F_i{X_i}^2=202250$

$\overline{X}=\frac{\sum F_i{X}_i}{\sum F_i}=\frac{3100}{50}=62$
Standard Deviation,
 $$\begin{gathered} \sigma =\sqrt{\frac{\sum F_i{X_i}^2}{\sum F_i}-\overline{X}} \\ =\sqrt{\frac{202250}{50}-62} \\ =\sqrt{4045-62} \\ =\sqrt{3983} \\ =63.11 \end{gathered}$$
Regards,