Example: Calculate median from the following data.

 

Value	Frequency	Value	Frequency
0—4	328	30—39	598
5—9	350	40—49	524
10—19	720	50—59	378
20—29	664	60—69	244

Solution: Computation of Median    

 

Class-interval	Frequency	Cumulative  frequency
0— 4	328	328
5— 9	350	678
10—19	720	1,398
20—29	664	2,062
30—39	598	2,660
40—49	524	3,184
50—59	378	3,562
60-69	244	3,806

Median is the value of (3806/2) or 1903th  item which lies in 20-29 group. This is a case of inclusive class-intervals. They should be made exclusive and the median group should be deemed to be in 19.5—29.5 group. Thus the value of l1 would be 19.5 and not 20.