A math convention and an engineering convention were being held in the same city. Consequently, a bunch of mathematicians and a bunch of engineers were on the same train headed for the city. Each of the engineers had his/her train ticket. The group of mathematicians had only ONE ticket for all of them. The engineers started laughing and snickering.
Then, one of the mathematicians said “here comes the conductor” and then all of the math majors went into the bathroom. The engineers were puzzled. The conductor came aboard and said “tickets please” and got tickets from all the engineers. He then went to the bathroom and knocked on the door and said “ticket please” and the mathematicians stuck the ticket under the door. The conductor took it and then the mathematicians came out of the bathroom a few minutes later. The engineers were dumbfounded.
So, on the way back from the convention, the group of engineers had one ticket for the group. They started snickering at the mathematicians, for the whole group had no tickets amongst them. Then, the mathematicians’ lookout said “Conductor coming!”. All the mathematicians went to the bathroom. All the engineers went to another bathroom. Then, before the conductor came on board, one of the mathematicians left the bathroom, knocked on the other bathroom, and said “ticket please.”