Posted by Lisa on .
In a 1970’s game show, a contestant was given a choice of three doors of which one contained a prize. The other two doors contained gag gifts like a chicken or a donkey. After the contestant chose an initial door, the host of the show then revealed an empty door among the two unchosen doors, and asks the contestant if he or she would like to switch to the other unchosen door. The question is should the contestant switch. Does the probability of winning increase by switching to the remaining door?

Probability 
Reiny,
This is often called the "Monty Hall" problem
Here is one explanation of the solution.
http://coastaltech.com/monty.htm