"How are three people going to travel on only one ticket?" asks an engineer.

"Watch and you'll see," answers an accountant.

They all board the train. The engineers take their respective seats but all three accountants 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 engineers saw this and agreed it was quite a clever idea. So after the conference, the engineers decide to copy the accountants on the return trip and save some money (knowing that accountants are clever with money). When they get to the station, they buy a single ticket for the return trip. To their astonishment, the accountants don't buy a ticket at all.

"How are you going to travel without a ticket?" says one perplexed engineer. "Watch and you'll see," answers an accountant.

When they board the train, the three accountants cram into a restroom and the three engineers cram into another one nearby. The train departs. Shortly afterward, one of the accountants leaves his restroom and walks over to the restroom where the engineers are hiding. He knocks on the door and says, "Ticket, please."