Fill ’er up! In a recent month, 88% of automobile drivers filled their vehicles with regular gasoline, 2% purchased midgrade gas, and 10% bought premium gas.18 Of those who bought regular gas, 28%

paid with a credit card; of customers who bought midgrade and premium gas, 34% and 42%, respectively, paid with a credit card. Suppose we select a customer at random.

(a) Draw a tree diagram to represent this situation.

(b) Find the probability that the customer paid with a credit card. Show your work.

(c) Given that the customer paid with a credit card, find the probability that she bought premium gas. Show your work.