[
Three engineers and three scientists were traveling by train to a
conference. The scientists went to the ticket window and bought three
one-way tickets. The engineers bought only one. The scientists
remarked that there were three engineers but only one ticket. The
engineers said to watch.

Right before the train left the three engineers crammed into one rest
room. When the conductor came through to collect tickets he checked
the rest room and, seeing it occupied, said "Ticket please." One of
the engineers cracked open the door and handed out the ticket, which
the conductor validated. After a few minutes the engineers returned to
their seats. The scientists were amazed, and said they'd try it on the
way back.

On the way back after the conference, the engineers and scientists met
at the ticket window again. The scientists said "we know what to do"
and bought only one ticket. But the engineers didn't buy any! Once
again the scientists were perplexed. The engineers said "wait and
see."

As the train left the station the scientists got up and crammed
themselves into a rest room. The engineers did the same. After a few
minutes, before the conductor appeared, one of the engineers came out
of their wash room and knocked on the door where the scientists were
and said "Ticket please!"
]