A firm has monitored duration of long-distance telephone calls placed by its employees to aid it decide which lonng-distance package to purchase. The duration of calls was found to be exponentially distribution, with mean call length of 5 minutes.
(a) Determine the probability a call lasts more than 2 minutes?
(b) Determine the probability a call lasts between 5 and 8 minutes?
(c) If a call has lasted 3 minutes, determine the probability it lasts an additional 4 minutes?