A survey was made of 100 customers in a department store. Sixty of the 100 indicated they visited the store because of a newspaper advertisement. The remainder had not seen the ad. A total of 40 customers made purchases; of these customers, 30 had seen the ad. (a) What is the probability that a person who did not see the ad made a purchase? (b) What is the probability that a person who saw the ad made a purchase