C.I	0-10	10-20	20-30	30-40	40-50
frequency	3	5	8	3	1

Solution:

class	$x_{i}$	$f_{i}$	$f_{i}x_{i}$	$d_{i}=\frac{x_{i}-a}{h}$	$f_{i}d_{i}$	$d_{i}^{2}$	$f_{i}d_{i}^{2}$
0-10	5	3	15	-2	-6	4	12
10-20	15	5	75	-1	-5	1	5
20-30	25	8	200	0	0	0	0
30-40	35	3	105	1	3	1	3
40-50	45	1	45	2	2	4	4
		20 …