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Graphing Statistics & Data
A frequency polygon, like the histogram, is a graphical display of class frequencies. However, instead of using bars or rectangles like a histogram, in a frequency polygon each class frequency is plotted as a dot at the class midpoint, and the dots are connected by a series of line segments.

Construction of a frequency polygon begins by scaling class midpoints along the horizontal axis and the frequency scale along the vertical axis. A dot is plotted for the associated frequency value at each class midpoint. Connecting these midpoint dots completes the graphs.

The following scores where obtained in a statistics exam:

 Class interval [50,60) [60,70) [70,80) [80,90) [90,100) Class value xi 55 65 75 85 95 Frequency fi 1 4 6 5 2

Display the results in a frequency polygon.

In this problem all the class intervals are of equal width and so first histogram could be drawn and then the middle point joined to get the frequency polygon.