Question

Calculate the mean by step-deviation method.
Class
10-15
15-20
20-25
25-30
30-35
35-40
Frequency
10
15
20
12
10
5​

Answer 1

Answer:

Let the assumed mean be A= 25 and h= 5.

Calculation of Mean

Variable

x

i

Frequency

f

i

Deviations

d

i

=x

i

−25 u

i

=

25

x

i

−25

f

i

u

i

5 20 -20 -4 -80

10 43 -15 -3 -129

15 75 -10 -2 -150

20 67 -5 -1 -150

25 72 0 0 0

30 45 5 1 45

35 39 10 2 78

40 9 15 3 27

45 8 20 4 32

50 6 25 5 30

N=∑f

i

=384

∑f

i

u

i

=−214

We have,

N= 384 , A= 25, h= 5 and ∑f

i

u

i

= -214

∴Mean=

X

=A+h[

N

1

∑f

i

u

i

]

⇒Mean=25+5×(

384

−214

)=25−2.786=22.214