1. find group median

class interval frequency

0.5-5.5 6

5.5-10.5 20

10.5-15.5 18

15.5-20.5 4

2. Find group median class interval frequency

7.5-8.5 1

8.5-9.5 2

9.5-10.5 4

10.5-11.5 2

11.5-12.5 1