[2+2 wannabe]

the ol' monty python game

<font color="white">your odds of picking the right one before the "goat" is shown is 1/3 (3 doors to pick from) - after the goat is shown your odds are 1/2 (only 2 doors and one is the prize one is goat). thus, if you switch, your odds are 1/2, and if you don't, your odds are 1/3.</font>