Use the data in Example 5.3 to find the probability that a customer purchases fuel or pays by debit card.

The probability that one (and by implication, both) of these outcomes occurs is based on the relative frequency of all the people who are in one or other category. This implies that we should add the number of customers who purchased fuel to the number of customers who paid by debit card, and divide the result by the total number of customers in the survey.