Here, the class intervals are discontinuous. Hence, first we convert the class intervals to continuous class intervals and then find mid-points of each class interval. We do this by adding 0.5 to each upper limit and subtracting 0.5 from each lower limit.

`{:("Class Interval","Exclusive","Mid-value of Class","Frequency"),(" "5-10,4.5-10.5," "7.5," "7),(" "11-16,10.5-16.5," "13.5," "13),(" "17-22,16.5-22.5," "19.5," "8),(" "23-28,22.5-28.5," "25.5," "12),(" "29-34,28.5-34.5," "31.5," "10):}`

Now, taking the mid-values of class intervals on the X-axis and the corresponding frequencies on the Y-axis, we draw a frequency polygon as shown in the Fig. 9.3.