Three engineers and three mathematicians were traveling to a conference by train.
When they arrived at the train station, the three mathematicians each bought a ticket and then they watched as the three engineers bought only a single ticket between them.
Looking very puzzled, one of the mathematicians asked the engineers: “How are three people going to travel on only one ticket?”
“Watch and you will see,” answered one of the engineers.
A few minutes later, their train arrived at the platform, and they all got on board.
The mathematicians found seats in one of the carriages, but were curious to see all three of the engineers cramming themselves into one of the restrooms and closing the door behind them.
Shortly after the train had left the station, the conductor came around collecting tickets. He knocked on the restroom door and said, “Ticket, please”. The door opened just a crack and a single arm emerged with a ticket in hand. The conductor took the ticket and moved on to the next carriage.
The mathematicians saw this and agreed that it was quite a clever idea.
So after the conference, the mathematicians decided to copy the engineers on the return trip and save some money (being clever with money, and all that).
When they got to the station, they bought a single ticket for the return trip, but to their astonishment, the engineers don’t buy a ticket at all.
“How on earth are you going to travel without a ticket?” asked one perplexed mathematician.
“Watch and you will see,” answered an engineer.
When they boarded the train, the three mathematicians crammed into one restroom and the three engineers crammed into another one nearby.
The train left the station and sShortly afterwards, one of the engineers left his restroom and walked over to the restroom where the mathematicians were hiding.
He knocked on the door and said, “Ticket, please”.
Image used under a Collective Commons License from: https://commons.wikimedia.org/wiki/File:Metropolitan_Railway_carriage_(first_class_interior)_(9129237231).jpg