The first joke below is a variant on a recent joke that has been circulating. The version I modified had a different group being fooled in the end, but somehow this version seems more appropriate.

Two groups of students, math and engineering, boarded a train that was headed for a technical convention. Each of the math majors had a ticket, but their engineering counterparts had only one ticket between them.

The math majors were snickering at this when an engineering student shouted, "Here comes the conductor!" With that, all the engineering majors squeezed into a bathroom. The intrigued math students watched as the conductor collected their tickets, then knocked on the bathroom door and said, "Ticket please." The conductor took the single ticket that was passed under the door and left.

Not to be outdone, the math students boarded the returning train but this time they had no ticket. The engineers laughed.

When the engineer lookout yelled, "Conductor coming!" all the engineers crowded into one bathroom, while the math majors piled into another. Then, before the conductor entered the car, one of the math majors came out of his bathroom and knocked on the engineers' bathroom door.

"Ticket please," he said.

This next joke appeared in the "Laughter, The Best Medicine" section of Reader's Digest (contributed to the magazine by Harold Teng).

Once, a mathematician, a biologist and a physicist were sitting in a sidewalk cafe when they noticed two people going into the house across the street. A while later they saw three people coming out.

The physicist says, "Our first count wasn't accurate."

The biologist concludes, "They must have reproduced!"

But the mathematician says, "Now if exactly one person enters the house, it will be empty again."

I don't know where the next one originates; it was sent to me by a colleague.

A linguistics professor was lecturing to his class one day. "In English," he said, "a double negative forms a positive. In some languages though, such as Russian, a double negative is still a negative." "However," he added, "there is no language wherein a double positive can form a negative."

A voice from the back of the room piped up, "Yeah, right! "