Here is the classic Monty Hall problem: Before you are three closed doors. Behind one of the doors is an all-expense paid trip to anywhere in the world.

Here is the classic Monty Hall problem: Before you are three closed doors. Behind one of the doors is an all-expense paid trip to anywhere in the world. Behind each of the other two doors is a postage stamp. First, you select a door. I won't open that one, but I will open one of the other two. In fact, behind one or both of the other doors is a stamp, and I'll open one that shows you a stamp. Next you have a choice of staying with your original choice or switching to the other door that is still closed. I'll open the door you finally settle on and you can take what is behind it. What is the best strategy, to stay or switch, or does it matter? Extensions of the problem and a complete solution are included. This mathematically rich problem was originally developed for the Project Discovery Mathematics by Inquiry institutes for middle grades teachers taught in 1992 - 1994 at Ohio State University. Project Discovery was co-funded by the Ohio Board of Regents and the Statewide Systemic Initiative (SSI) program of the National Science Foundation. (author/sw)