The blood type O negative is called the ‘‘universal donor’’ type, because it is the only blood type that may safely be transfused into any person. Therefore, when someone needs a transfusion in an emergency and their blood type cannot be determined, they are given type O negative blood. For this reason, donors with this blood type are crucial to blood banks. Unfortunately, this blood type is fairly rare; according to the Red Cross, only 7% of U.S. residents have type O negative blood. Assume that a blood bank has recruited 20 donors.

a. What is the probability that two or more of them have type O negative blood?

b. What is the probability that fewer than four of them will have type O negative blood?

c. Would it be unusual if none of the donors had type O negative blood?

d. What is the mean number of donors who have type O negative blood?

e. What is the standard deviation of the number of donors who have type O negative blood?