Three PhDs and three MDs are going to a conference and must travel by train to get there. At the station, the three MDs buy their three tickets and watch as the three PhDs buy only a single ticket. "How are three people going to travel on only one ticket?" says one MD. "Just watch and you'll see," answers a PhD.

They all board the train and the MDs take their seats and watch as all three PhDs cram into a restroom and close the door behind them. Thetrain departs and shortly afterward, the conductor comes around collecting tickets. He knocks on the restroom door and says "Ticket,
please." The door opens just a crack and a single arm emerges with a ticket in hand. The conductor takes it and moves on.

The MDs see all this and agreed it is quite a clever idea. So after the conference, the MDs decide to copy the PhDs on the return trip and save some money (managed care and all that). When they get to the station, they buy a single ticket for the return trip. But to their astonishment, the PhDs don't buy a ticket at all.

"How are you going to travel without a single ticket?" says one MD. "Just watch and you'll see," answers a PhD.

They board the train. The three MDs cram into a restroom compartment and the three PhDs cram into an another one nearby. The train departs. Shortly afterward, one of the PhDs leaves his restroom, walks over to the MDs stall, knocks on the door and says, "Ticket, please".