practice problem

A consumer electronics company with 100 stores sells multiple brands of cell phones. Forty of their stores carry 20% iPhones and 80% other brands, and sixty of their stores carry 50% iPhones and 50% other brands. If a store is selected at random, and a phone is purchased from that store at random, what is the marginal probability the phone purchased is an iphone? (Answers are rounded.) O .35 O .32 .38 O .5