Marks scored by students of class 10A and 10B in a particular class test are as follows:

Marks	No. of students of 10A	No. of students of 10B
1 - 5	1	2
6 - 10	3	6
11 - 15	8	3
16 - 20	9	10
21 - 25	4	7
26 - 30	5	6
31 - 35	6	4
36 - 40	4	2

Draw their frequency polygons on the same graph.

The following frequency distribution is discontinuous, to convert it into continuous frequency distribution,

Adjustment factor = $\dfrac{\text{(Lower limit of one class - Upper limit of previous class)}}{2}$

= $\dfrac{\text{(6 - 5)}}{2} = \dfrac{1}{2} = 0.5$

Subtract the adjustment factor (0.5) from all the lower limits and add the adjustment factor (0.5) to all the upper limits.

Continuous frequency distribution for given data is :

Steps to draw frequency polygon :

1. Take 1 cm along x-axis = 4 units.

2. Take 1 cm along y-axis = 1 units.

3. Find the mid-points of class-intervals.

4. Find points corresponding to given frequencies of classes and the mid-points of class-intervals, and plot them.

5. Join consecutive points by line segments.

6. Join first end point with mid-point of class -5.5 - 0.5 with zero frequency and join the other end with mid-point of class 40.5 - 45.5 with zero frequency.

The required frequency polygon is shown alongside.