The owner of a fast-food restaurant ascertains the ages of a sample of customers. From these data, the owner constructs the frequency distribution shown. For each class interval of the frequency distribution, determine the class midpoint, the relative frequency and the cumulative frequency.

Class Interval ....... Frequency
0–under 5 ...........          6
5–under 10 .........          8
10–under 15 ........      17
15–under 20 ........      23
20–under 25 .......       18
25–under 30 .......       10
30–under 35 .......        4

What does the relative frequency tell the fast-food restaurant owner about customer ages?