There are two big conferences in NY....one for Engineers and one for Lawyers. They are both being held in the same building downtown. On the first day of the conference, two groups run into each other at the train station and chat while waiting in line to buy tickets into the city.
When they reach the counter, the three lawyers each buy tickets and watch as the three Engineers buy only a single ticket. "How are three people going to travel on only one ticket?" asks a lawyer. "Watch and you'll see," answers an Engineer.
They all board the train. The lawyers take their respective seats, but all three Engineers 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 lawyers saw this and agreed it was quite a clever idea.
So after the conference, the lawyers decide to copy the Engineers on the return trip and save some money (recognizing the Engineers' superior intellect). When they get to the station, they buy a single ticket for the return trip. To their astonishment, the Engineers don't buy a ticket at all. "How are you going to travel without a ticket?" says one perplexed lawyer. "Watch and you'll see," answers an Engineer.
When they board the train the three lawyers cram into a restroom and the three Engineers cram into another one nearby. The train departs. Shortly afterward, one of the Engineers leaves his restroom and walks over to the restroom where the lawyers are hiding. He knocks on the door and says, "Ticket, please."