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Frequency Polygon :- A frequency polygon is a polygon representing a frequency distribution. The class mark of a class is taken along x-axis and corresponding frequencies along y-axis and the plotted points are joined. The polygon is completed by joining the points at each end to the mid values of the immediate lower and higher class of interval on x-axis.

It is also drawn by joining the mid points of the upper horizontal sides of the adjacent rectangles of a histogram by straight lines and the polygon is completed by joining the points at each end to the mid value of the immediate lower and higher class interval on x-axis. 

Example – 2. For the following frequency distribution draw a frequency polygon.

Solution :-  Here the class intervals are inclusive. So, first let us convert it to exclusive form as under :

Fig. – 2.

Cumulative Frequency Curve  Or  Ogive :- The curve obtained by plotting upper limit  of the class against cumulative frequencies is called cumulative frequency curve or ogive.

When cumulative frequencies are calculated from lower values of the data, it is called less than cumulative frequency and the curve is called less than cumulative frequency curve. When cumulative frequencies are calculated from upper values of the data, it is called more than cumulative frequency and the curve is called more than cumulative frequency curve.