Studies have shown that 28% of people do all of their Christmas shopping before Thanksgiving each year. Let X be the number of people you have to ask until you find somebody who has finished all of their Christmas shopping before Thanksgiving, assuming each person is independent of the others.
a. What is the expected number of people you will have to ask until you find somebody who has finished her Christmas shopping before Thanksgiving?
b. If each interview takes approximately 5 minutes, how much time should you expect to have to spend total?
c. What is the probability that you will have to ask more than 10 people?