Question

3. Following table gives frequency distribution of saplings planted by different housing societies in a
particular locality :
Number of saplings
10-15
15-20
20 25
25-30
- 3035
35-40
Number of societies
2
7
9
8
4
Find mean number of saplings planted by housing societies by step deviation method. (4 marks)​

Answer 1

Answer:

Consider the following table, to calculate mean by "step deviation method":

x

i

=mid value of class interval

Assumed mean a=27.5

class interval c=5

ci f

i

x

i

d

i

=

c

x

i

−a

f

i

d

i

10-15 2 12.5

5

12.5−27.5

=-3 -6

15-20 7 17.5 -2 -14

20-25 9 22.5 -1 -9

25-30 8 27.5 0 0

30-35 6 32.5 1 6

35-40 4 37.5 2 8

N=Σf

i

=36

Σf

i

d

i

=−15

Mean

x

=a+

N

Σf

i

d

i

×c

∴

x

=27.5+

36

−15

×5=25.42

Hence, option A is corect.