Three engineers and three accountants are travelling by train to a conference. At the station, the three accountants each buy a ticket and watch as the three engineers only buy one ticket.

"How are three people going to travel on only one ticket?" one of the accountants asks. "Watch and you'll see," answered an engineer.

They all board the train. The accountants take their respective seats but all three engineers cram into a rest room 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: "Tickets, 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 accountants see this and agree it is a clever idea. So after the conference, the accountants decide to copy the engineers on the return trip and save some money.

When they get to the station, they buy one 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 accountant.

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

When they board the train all three accountants cram into a restroom and the three engineers cram into another one nearby.

The train departs. Shortly afterwards, one of the engineers leaves his restroom and walks over to the restroom where the accountants are hiding. He knocks on the door and says: "Tickets, please.