A mathematician and an engineer are sitting next to each other on a long flight. The mathematician leans over to the engineer and asks if he would like to play a fun game. The engineer just wants to take a nap, so he politely declines and rolls over to the window to catch a few winks.
The mathematician persists and explains that the game is real easy and lots of fun. He explains, "I ask you a question, and if you don't know the answer, you pay me Rs.500. Then you ask me a question, and if I don't know the answer, I'll pay you Rs.500."
Again, the engineer politely declines and tries to get to sleep. The mathematician, now somewhat agitated, says, "Okay, if you don't know the answer, you pay me Rs.500, and if I don't know the answer, I'll pay you Rs.5000!"
This catches the engineer's attention, and he sees no end to this torment unless he plays, so he agrees to the game. The mathematician asks the first question. "What's the distance from the earth to the moon?"
The engineer doesn't say a word, but reaches into his wallet, pulls out a Rs.500 and hands it to the mathematician Now, it's the engineer's turn. He asks the mathematician "What goes up a hill with three legs and comes down on four?"
The mathematician looks up at him with a puzzled look. He takes out his laptop computer and searches all of his references. He taps into the air phone with his modem and searches the net and the Library of Congress. Frustrated, he sends e-mail to his co-workers all to no avail.
After about an hour, he wakes the engineer and hands him Rs.5000. The engineer politely takes the Rs.5000 and turns away to try to get back to sleep.
The mathematician then hits the engineer, saying, "What goes up a hill with three legs, and comes down on four?" The engineer calmly pulls out his wallet, hands the mathematician Rs. 500, and goes back to sleep.