One day two maths students and two science students of university went out for a seminar.

They decided to go there by train. So science students obtained two tickets for both. But maths students obtained only one ticket. Half way of their journey ticket checkers came at them checking tickets of the rest. Then both maths students went to the toilet and closed the door under the rose. After a little while ticket checkers came to the door and knocked at it asking for ticket. Then one of the two students put his hand out under the door and gave the ticket.

When they came back to university after the seminar maths students obtained one ticket like they did before. But two science students didn’t obtain any. Half way of their journey ticket checkers came like before. Then two maths students went to the toilet and closed the door like they did before. Science students followed them and knocked at the door asking for tickets. Thinking that the checkers have come one of them gave the ticket. Science students got the ticket and entered to the next room.