First, put these in order with their frequency if more than one).
0, 1 (3), 3, 5 (2), 6 (2), 7 (2), 11, 12, 14 (2), 15, 17, 18 (2), 19
The values range from 0 to 19, so the natural way to classify them would be to split them into 0-3, 4-7, 8-11, 12-15, 16-19. We have:
Class 1: 0 1 1 1 3; Median: 1
Class 2: 5 5 6 6 7 7; Median: 6
Class 3: 11; Median: 11
Class 4: 12 14 14 15; Median: 14
Class 5: 17 18 18 19; Median: 18
The medians are the midpoints of the data in each class. Below are the data values 0 to 19 and their absolute frequencies followed by their relative and cumulative frequencies.
Class 1
0 1 0.2 0.2
1 3 0.6 0.8
2 0 0 0.8
3 1 0.2 1.0
Class 2
4 0 0 0
5 2 0.33 0.33
6 2 0.33 0.67
7 2 0.33 1.00
Class 3
8 0 0 0
9 0 0 0
10 0 0 0
11 1 1 1
Class 4
12 1 0.25 0.25
13 0 0 0.25
14 2 0.5 0.75
15 1 0.25 1.00
Class 5
16 0 0 0
17 1 0.25 0.25
18 2 0.50 0.75
19 1 0.25 1.00
Class 2 has the greatest frequency (6) and class 3 the least (1).