The waiting time before service in a bank is exponentially distributed with a mean waiting time of 5 minutes. a. What is the median waiting time. b. You enter the bank and find that your friend has...

The waiting time before service in a bank is exponentially distributed

with a mean waiting time of 5 minutes.
a. What is the median waiting time.
b. You enter the bank and find that your friend has been waiting in the

queue for service for past 2 minutes. Upon your arrival what is the

probability that your friend will wait for another 4 minutes?
c. What is the mean and variance of the waiting time in the bank?