Question

Calculate the Mean Deviation using mean and Standard Deviation for the following distribution.

Classes	Frequencies
20 – 40	3
40 – 80	6
80 – 100	20
100 – 120	12
120 – 140	9
Total	50

Answer 1

Classes	Frequency	m	A = 90 d = X – A				fd'	d'2	fd'2
20 – 40	3	30	– 60	60	180	– 6	– 18	36	108
40 – 80	6	60	– 30	30	180	– 3	– 18	9	54
80 – 100	20	90	0	0	0	0	0	0	0
100 – 120	12	110	20	20	240	2	24	4	48
120 – 140	9	130	40	40	360	4	36	16	144

Mean Deviation from mean