4. Calculate Mean deviation, Coefficient of M.D. from the following grouped data

Class	Frequency
10 - 20	15
20 - 30	25
30 - 40	20
40 - 50	12
50 - 60	8
60 - 70	5
70 - 80	3

Solution:
Mean deviation :
Mean `bar x=(sum f x)/(sum f)`

`=3080/88`

`=35`

Class `(1)`	`f` `(2)`	Mid value (`x`) `(3)`	`f*x` `(4)=(2)xx(3)`	`|x-bar x|=|x-35|` `(5)`	`f*|x-bar x|` `(6)=(2)xx(5)`
10 - 20	15	15	225	20	300
20 - 30	25	25	625	10	250
30 - 40	20	35	700	0	0
40 - 50	12	45	540	10	120
50 - 60	8	55	440	20	160
60 - 70	5	65	325	30	150
70 - 80	3	75	225	40	120
---	---	---	---	---	---
--	`n=88`	--	`sum f*x=3080`	--	`sum f*|x-bar x|=1100`

Mean deviation of Mean
`delta bar x = (sum f*|x - bar x|)/n`

`delta bar x = 1100/88`

`delta bar x = 12.5`


Coefficient of Mean deviation `=(delta bar x)/(bar x)`

`=12.5/35`

`=0.3571`

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