In a certain month, 88% of automobile drivers filled their vehicles with regular gasoline, 2% purchased midgrade gas, and 10% bought premium gas. 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 model this chance process.

b. Find the probability that the customer paid with a credit card.

c. Suppose the chosen customer paid with a credit card. What’s the probability that the customer bought premium gas?