A little story

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