So there are a group of engineers and a group of mathematicians heading to a conference They are sitting on a train together when both groups spot the train's ticket collector coming down the aisle. Quickly two of the engineers scuttle into the washroom, leaving the mathematicians confused. After the collector stamps all the mathematicians tickets he approaches the washroom and knocks. ""Ticket please"" A ticket slides under the door, and is stamped by the collector and returned. ""Thank you!"" replies the collector. Both groups then enjoy lots of nerdy things at the conference. On the way home the mathematicians had learned the engineers trick. As the train pulls away the mathematicians all hide in the washroom, using the scam they had seen the engineers pull on the way there. One engineer stands up and then knocks on the washroom declaring ""Ticket please!"" After which the mathematicians slides his ticket under the door. The mathematicians pile out of the washroom and return to their seats with a grin on their faces. Soon after the ticket collector enters the car, at which time all the engineers cram themselves into the washroom.