An Ad Agency Is Developing a Campaign to Promote a Business

Multiple Choice

An ad agency is developing a campaign to promote a business opening in a new mall development.To develop an appropriate mailing list,they decide to purchase lists of credit card holders from MasterCard and American Express.Combining the lists,they find the following: 40 percent of the people on the list have only a MasterCard and 10 percent have only an American Express card.Another 20 percent hold both MasterCard and American Express.Finally,30 percent of those on the list have neither card.Suppose a person on the list is known to have a MasterCard.What is the probability that person also has an American Express Card?

A) .20
B) .33
C) .18
D) .70
E) .90