At the maintenance shop one has to go to station A first and then to station B (in that order) before leaving. The waiting time at station A and B is exponentially distributed with means 6 and 3 minutes (i.e. on an average it takes 6 minutes to get served at station A and 3 minutes to get served at station B). When you arrive at the shop there is already somebody at station A but station B is empty. How long, on an average, will you take to get served at both the stations?
Answer: 16 minutes