A recent survey states that 48% of mobile devices are iPhones. In order to learn more about how the iPhone works, a student starts asking random people on campus if they use an iPhone. Assume that the individuals on campus are independent.
a. If he surveys 20 people, what is the probability he finds exactly 2 people who use an iPhone?
b. If he surveys 20 people, what is the probability he finds at least 2 people who use an iPhone?
c. If he surveys 20 people, what is the probability he finds fewer than 2 people who use an iPhone?
d. How many students would he have to ask to be at least 90% certain of finding at least one person who uses an iPhone?