Question

The class marks of a frequency distribution are: 27, 32, 37, 42, 47, 52, 57, 62, 67, 72 and 77. Find the class size and true class limits.

Answer 1

The class marks are uniformly spread.
∴ The class size is the difference between any two consecutive class marks.
Class size 
= 32 - 27
= 5
The lower limit of the first class

= `27 - (5)/(2)`
= 27 - 2.5
= 24.5
The upper limit of the first class

= `27 + (5)/(2)`
= 27 + 2.5
= 29.5
Thus, the first class interval is 24.5 - 29.5
Similarly, we can find the class limits of all the class marks given.

Class Marks	Class limits
27	24.5 - 29.5
32	29.5 - 34.5
37	34.5 - 39.5
42	39.5 -- 44.5
47	44.5 - 49.5
52	49.5 - 54.5
57	54.5 - 59.5
62	59.5 - 64.5
67	64.5 - 69.5
72	69.5 - 74.5
77	74.5 - 79.5