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 21: 11, 63, 10, 53, 16, 6, 27, 36, 68, 1, 52, 68, 42, 36, 23, 68, 27, 19, 30, 3, 44

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 10, starting at 0: 0–9, 10–19, 20–29, 30–39, 40–49, 50–59, 60–69