Find the mean deviation about the mean for the following data : class 30-40 40-50 50-60 60-70 70-80 80-90 90-100 Frequency 3 7 12 15 8 3 2

Find the mean deviation about the mean for the following data :

class

30-40

40-50

50-60

60-70

70-80

80-90

90-100

Frequency

3

7

12

15

8

3

2

we make the following table from the given data:

class	Frequency f_i	Mid-points x_i	f_ix_i
30-40	3	35	105
40-50	7	45	315
50-60	12	55	660
60-70	15	65	975
70-80	8	75	600
80-90	3	85	255
90-100	2	95	190
	50		3100

Therefore,

class	Frequency f_i	Mid-points x_i	f_ix_i
30-40	3	35	105	27	81
40-50	7	45	315	17	119
50-60	12	55	660	7	84
60-70	15	65	975	3	45
70-80	8	75	600	13	104
80-90	3	85	255	23	69
90-100	2	95	190	33	66
	50		3100		568

Thus, the required mean deviation about the mean is

1