Math vs Engineering

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