Question

Construct a frequency polygon for the following data:

Class-Intervals	10-14	15-19	20-24	25-29	30-34
Frequency	5	8	12	9	4

Answer 1

The class intervals are inclusive. We will first convert them into the exclusive form.

Class-Interval	Frequency
9.5-14.5	5
14.5-19.5	8
19.5-24.5	12
24.5-29.5	9
29.5-34.5	4

Steps:

1. Draw a histogram for the given data.
2. Mark the mid-point at the top of each rectangle of the histogram drawn.
3. Also, mark the mid-point of the immediately lower class-interval and the mid-point of the immediately higher class-interval.
4. Join the consecutive mid-points marked by straight lines to obtain the required frequency polygon. 

The required frequency polygon is as follows: