A shop owner did a survey to determine the ages of shoppers who made purchases in the shop. The results for one afternoon are shown. How many shoppers were between the ages of 20 and 30, including 20 and 30?
13, 19, 20, 30, 30, 31, 38, 48, 50, 52, 55, 56, 65, 67, 69, 69, 70, 75