An important part of the customer-service responsibilities of a telephone company relate to the speed with which troubles in residential service can be repaired. Suppose that past data indicate that the likelihood is 0.70 that troubles in residential service can be repaired on the same day. If a sample of 100 troubles is selected, what is the probability that the proportion repaired on the same day is

(a) between 0.70 and 0.75?
(b) at least 0.70?
(c) between 0.60 and 0.80?
(d) What would be your answers to (a)-(c) if n = 50?