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Find the Mean of the Following Distribution by Step Deviation Method: - Mathematics

Find the mean of the following distribution by step deviation method:

Class Interval 20-30 30-40 40-50 50-60 60-70 70-80
Frequency 10 6 8 12 5 9
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Solution

Class
interval
Frequency
(f)
Class mark
(x)
d = `(x - A)/h`  (A = 55) fd
20-30 10 25 -3 -30
30-40 6 35 -2 -12
40-50 8 45 -1 -8
50-60 12 A = 55 0  0
60-70 5 65 1 5
70-80 9 75 2 18
Total 50     -27

Here A = 55, h = 10

Mean = `A + (sumfd)/(sumf) xx h`

`= 55 + (-27)/50 xx 10`

= 55 - 5.4

= 49.6

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