Look at the intervals. How many times does a given value get plotted in each value?
0 - 5: 4 <em> (1 value falls in the 0-5 interval)</em>
5 - 10: 8, 7, 7, 9 <em>(4 values fall in the 5-10 interval)</em>
10 - 15: 13, 14 <em>(2 values fall in the 10-15 interval)</em>
15 - 20: 19 <em>(1 value falls in the 15-20 interval)</em>
Next, draw a rectangle from each interval to the number of values that fall into that category.
Rectangle 1: (0,1) to (5,1)
Rectangle 2: (5,4) to (10, 4)
Rectangle 3: (10, 2) to (15, 2)
Rectangle 4: (15, 1) to (20, 1)