A blonde and a lawyer are sitting next to one another on a long flight.

Bored, and thinking he could have some fun with her, the lawyer leans over and offers to play a game.
"We take turns asking each other questions. If you cannot answer my question correctly, you must give me $10. If I cannot answer a question of yours correctly, I will give you $100. Deal?"
The blonde agrees to play, and they exchange a few simple questions, both getting correct answers.

Then the lawyer decides to ask some harder questions.
"What year did Albert Einstein create his Theory of Relativity?"
The blonde frowns for a minute or two, then reaches into her purse and wordlessly gives him $10.
"Okay, your turn."

She asks, "What goes up a hill with three legs and comes down with four?"

Stumped, the lawyer ponders for a while. It seemed like such a riddle, he even started asking other passengers, and the flight attendants. The blonde didn't protest, only sat in silence as he wracked his brain.
Despite his pride being on the line, after about forty minutes filled with serious contemplation, the lawyer finally gives up and pulls $100 out of his wallet for her.

"What was the answer, by the way?" He asked her.

The blonde wordlessly reaches into her purse and gives the lawyer $10.