The probability that your call to a service line is answered in less than 30 seconds is 0.75. Assume that your calls are independent.

a. If you call 10 times, what is the probability that exactly nine of your calls are answered within 30 seconds?

b. If you call 20 times, what is the probability that at least 16 calls are answered in less than 30 seconds?

c. If you call 20 times, what is the mean number of calls that are answered in less than 30 seconds?

d. What is the probability that you must call four times to obtain the first answer in less than 30 seconds?

e. What is the mean number of calls until you are answered in less than 30 seconds?