Question

Calculate the mean deviation about mean and standard deviation for the following distribution:

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

Answer 1

Calculation of mean deviation about mean:

Mean Deviation from A.M.

= \(\frac{\Sigma fd}{\Sigma f}\)

= \(\frac{998.4}{50}\)

= 19.96

Calculation of standard deviation from mean:

Classes	f	m	m - 90(d)	\(\frac{d}{10}(d')\)	fd'	fd
20 - 40	3	30	-60	-6	-18	108
40 - 80	6	60	-30	-3	-18	54
80 - 100	20	90	0	0	0	0
100 - 120	12	110	+20	+2	24	48
120 - 140	9	130	+40	+4	36	144
	N = 50				∑fd' = 24	∑fd' = 354

A.M.10