Question

Find the mean of following frequency distribution by using step-deviation method.

class interval 0-10,10-20,20-30,30-40, 40-50,50-60

Frequency 3,5,8,12,2,5​

Answer 1

Answer:

C.I. Frequency (f

i

) Mid-value(x) d

i

=

h

x−a

f

i

d

i

20−30 10 25 −2 −20

30−40 6 35 −1 −6

40−50 8 45 0 0

50−60 12 55 1 12

60−70 5 65 2 10

70−80 9 75 3 27

∑f

i

=50 ∑f

i

d

i

=23

Here, a=45 and h=10

∴ Mean =a+

∑f

i

∑f

i

d

i

×h

=45+

50

23

×10

=45+4.6=49.6