Time in post office
Question
A bank has 2 tellers. Andy enters the bank, while the two tellers are busy serving two other customers (Customer A and Customer B). Andy is next in line. The time a teller spends serving a customer has an Exponential(λ) distribution. Given this information:

a) What is the probability that Andy is the last of the 3 customers to finish being served?

b) What is the expected total time that Andy will need to spend at the bank?