The Game-Show Puzzle    
A famous puzzle, commonly known as the "Monty-Hall" problem after a well-know US game-show host. This puzzle is widely discussed  and argued about. 
Step 1
You are a contestant on a game show. The host shows you three boxes, labelled A, B, and C. Inside one of the boxes is a valuable prize. All you have to do to win is pick the right box. Let's say you pick box A.
Download the Game-Show program
Step 2
The host now opens one of the other boxes, say box C, and shows you that it is empty. You are now given the option of switching your choice to box B instead of box A., or you can stick with box A.
The Question
Should you stick with your first choice, or take opportunity to change your selection at Step 2? What are your chances of winning in each case?
Simple explanation
Detailed explanation