Free Republic

Forget Fermat’s last theorem. The most vexing challenge in mathematics just might be the Monty Hall problem. Monty Hall — born Monte Halparin — presented nearly 5,000 episodes of Let’s Make a Deal, the US game show that inspired the puzzle. It is an onion of a conundrum; layer after layer, and guaranteed to make you cry. The puzzle is this: a contestant faces three doors. Behind one of them is a big prize such as a Cadillac. Each of the other two doors conceals a booby prize such as a goat.

A man who was born in Canada, became a U.S. citizen, and stayed married to the same woman for almost 70 years died today. A true cultural icon of a better time, Monty Hall is gone now.

It’s about time we did the Monty Hall problem. Many of you will already know the answer, but read on anyway because it turns out to be an excellent example to demonstrate fundamental ideas in probability. Incidentally, I just did this yesterday to a group of surgical residents: you might be happy to know that none of them got the right answer. One even insisted—for a while—that I was wrong. Here’s the problem. Setup: Monty Hall shows you three doors, behind one of which is a prize, behind the other two is nothing. Monty knows which door hides the prize....