Draw a frequency polygon imposed on the histogram for the following distribution.
Class interval
10−20
20−30
30−40
40−50
50−60
60−70
70−80
80−90
Frequency
4
6
8
10
12
14
7
5
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Solution
Take the class-intervals along the X-axis and frequencies along the Y-axis with appropriate scale as shown. Now mark the mid points of the upper sides of the consecutive rectangles. We also make the midpoints of the assumed class intervals 0−10 and 90−100. The mid points are joined with the help of a ruler. The ends of the polygon are joined with the mid points of 0−10 and 90−100. Now, we get the frequency polygon.