You're waiting in line at the express checkout of grocery store. Three customers are waiting ahead of you and customer who was being served has just finished. The checkout time for an individual customer has an exponential distribution with mean 20 seconds.
A) Determine the probability that you will still be waiting for service to begin 2 minutes from now?
B) What is the probability that you will be completely checked out and heading for the parking lot 2 minutes from now?