Frequency Polygon 

A frequency polygon is very similar to a histogram and represents the graphical form of data.

A frequency polygon is used to show a cumulative frequency distribution or compare to sets of data. 

In a frequency polygon the number of observations is marked at the the midpoint of the interval with a single point, and a straight line connects each set of point.

Draw frequency polygons

First we begin with drawing histograms and follow the following steps:

Step 1:- Choose the class interval of each class and mark the values on horizontal axes.

Step 2:- Mark the mid value of each interval on the horizontal axes.

Calculate the class mark for each class interval. The formula for class mark is,

Class mark = (Upper limit + Lower limit)/2

Step 3:- Mark the frequency of the class on the vertical axes.

Step 4:- Corresponding to frequency of each class interval, mark a point at the height in the middle of the class interval. 

Step 5:- Join all the plotted points using a line segment.

Step 6:- The resulting representation is a frequency polygon.