Question

Draw a frequency polygon for the following data:

Marks	5 - 9	10 - 14	15 - 19	20 - 24	25 - 29	30 - 39
No. of students	7	11	15	22	18	5

Answer 1

We see that the class intervals are in an inclusive manner. We first need to convert them into exclusive manner.

Marks	No. of students
4.5 - 9.5	7
9.5 - 14.5	11
14.5 - 19.5	15
19.5 - 24.5	22
24.5 - 29.5	18
29.5 - 34.5	5

We take the class limits on the x-axis and the frequencies on the y-axis on suitable scales.

Now, find class marks of all the class intervals. Locate the points (x₁, y₁) on the graph, where x₁ denotes the class mark and y₁ denotes the corresponding frequency. Join all the points plotted above with straight line segments. Join the first point and the last point to the points representing class marks of the class intervals before the first class interval and after the last class interval of the given frequency distribution.

Here as the class limits do not start from 0, we put a kink between 0 and the lower boundary of the first class.