The time (in minutes) between telephone calls at an insurance claims office has the exponential probability distribution:
f(x) = 0.50e-.50x for x ≥ 0
a. What is the mean time between telephone calls?
b. What is the probability of 30 seconds or less between telephone calls?
c. What is the probability of 1 minute or less between telephone calls?
d. What is the probability of 5 or more minutes without a telephone call?