Show the following data by a frequency polygon.

Answer: Plot (100, 240), (300, 300), (500, 450), (700, 350), (900, 160) and join them, closing at (−100, 0) and (1100, 0)

Take class marks (electricity bill) on the X-axis and number of families on the Y-axis with a convenient scale. Plot the points and also the points (-100, 0) and (1100, 0), which are the class marks of the imaginary classes just before the first and just after the last class (frequency 0). Join all the points in order by line segments:

(-100, 0), (100, 240), (300, 300), (500, 450), (700, 350), (900, 160), (1100, 0)

The closed figure obtained with the X-axis is the required frequency polygon.