Six engineers and six mathematicians are attending a conference and are traveling by train.

One by one, each of the mathematicians goes up to the ticket counter and buys a ticket to the conference

But only one of the engineers does

The math majors started laughing and snickering.

The twelve get on the same car and one of the engineers stands at each end of the car

Now the mathematicians are really puzzled.

After a while, one of the look outs, yells, “Conductor!” On that cue, all the engineers pile into the rest room and lock the door.

The conductor enters the car and announces, “Tickets, please

Tickets!” He passes the mathematicians and punches each of their tickets

At the end of the car, he notices the restroom is occupied and knocks on the door, “Ticket, please.”

The ticket slides out from under the door, he punches it and slides it back, then leaves the car and continues to the next car.

The mathematicians look at each other and decide how clever the engineers were, and then wink at each other.

They all attend the conference and have a good time

Upon arriving at the train station, again only one of the engineers buys a ticket

The mathematicians do not buy any

This time the engineers start laughing and snickering.

This time all the mathematicians sit down and the engineers post their lookouts

One engineer, peers down a couple of cars and shouts, “Conductor!”

Immediately all the engineers pile into the rest room, while all the mathematicians pile into the other.

Just before the conductor gets there, one of the mathematicians slips out, runs down to the other restroom, knocks on the door and says, “Ticket, please.”