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

"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," answered 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 afterward, 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!"