Group numerical data into class intervals

Here are the values of the number of calls answered by staff at a call centre in a shift, for a sample of 25: 63, 60, 68, 17, 23, 82, 74, 66, 21, 67, 5, 35, 22, 44, 44, 59, 11, 15, 93, 55, 71, 88, 65, 0, 84

All listed values are whole numbers. Each interval includes both written endpoints; the next whole number starts the next interval

Use class intervals of width 20, starting at 0: 0–19, 20–39, 40–59, 60–79, 80–99