Three doctors and three nurses...

Three doctors and three nurses are traveling by train to a conference. At the station, the three doctors each buy tickets and watch as the three nurses buy only a single ticket. "How are three people going to travel on only one ticket?" asks a doctor.
"Watch and you'll see," answered a nurse. They all board the train. The doctors take their respective seats but all three nurses cram into a restroom and close the door behind them. Shortly after the train has departed, 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 doctors saw this and agreed it was quite a clever idea. So after the conference, the doctors decide to copy the nurses on the return trip and save some money (being clever with money, and all that). When they get to the station, they buy a single ticket for the return trip. To their astonishment, the nurses don't buy a ticket at all. "How are you going to travel without a ticket?" says one perplexed doctor.
"Watch and you'll see," answered a nurse. When they board the train the three doctors cram into a restroom and the three nurses cram into another one nearby. The train departs. Shortly afterward, one of the nurses leaves his restroom and walks over to the restroom where the doctors are hiding. He knocks on the door and says, Ticket, please."

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Brian Short
WORLDWIDE NURSE: The Internet's Nursing Directory
wwnurse.com/