Question

The class marks of a frequency distribution are 5, 10, 15, 20, 25, 30; find the class intervals.

Answer 1

Given: The class marks (midpoints) are 5, 10, 15, 20, 25, 30.

Step-wise calculation:

Let successive class marks differ by h = 10 – 5 = 5, so class-size = 5.

For equal contiguous class-intervals, half the class-size is `h/2` = 2.5.

For each class mark m, the class interval = m – 2.5 to m + 2.5.

Apply to each mark:

For m = 5 → 5 – 2.5 = 2.5 and 5 + 2.5 = 7.5 → 2.5 – 7.5

For m = 10 → 7.5 – 12.5

For m = 15 → 12.5 – 17.5

For m = 20 → 17.5 – 22.5

For m = 25 → 22.5 – 27.5

For m = 30 → 27.5 – 32.5

The class intervals are:

2.5 – 7.5

7.5 – 12.5

12.5 – 17.5

17.5 – 22.5

22.5 – 27.5

27.5 – 32.5