Question

The class marks of a frequency distribution are 15, 20, 25, ………. .Find the class corresponding to the class mark 20.

Answer 1

We know that

Class size = 20 – 15 = 5

Consider a as the lower limit of the required class

Upper limit can be written as a + 5

So we get

(a + (a + 5))/ 2 = 20

On further calculation

2a + 5 = 40

So we get

2a = 35

By division

a = 17.5

Upper limit a + 5 = 17.5 + 5 = 22.5

Therefore, the required class is 17.5-22.5

Answer 2

Given, CM= 15,20,25,30,35.....
Since the CM are of equal width, then class size= 20-15=5
Using the formula:
a+(h/2) and a-(h/2), Where a= CM and h=class size
Substituting,
20+(5/2)=20+2.5=22.5
20-(5/2)=20-2.5=17.5
Therefore, class (CM=20) is 22.5-17.5
Again,
25+(5/2)=25+2.5=27.5
and 25-(5/2)=25-2.5=22.5
Therefore, Class= 22.5-27.5