Let's Make a Deal

Let's say you were on Let's Make a Deal and Monty Hall offered you a choice of three doors. Behind one door is a car, the other two doors have goats behind them. You choose a door. Monty then shows you a goat behind one of the remaining doors and asks if you want to change your mind. Does it make a differance what you do?

There is a correct answer and most people get it wrong.

You might reason there was a one in three chance of you being right originally and now it changed to one and two and each door is equally valid.

That is incorrect. The door you picked had a one and three chance in being right. The other remaining door has a two in three chance of being right.

This is only valid if Monty plays fair and knows where the car is and always opens one of the other doors to show you a goat.

Many people, including mathematicians, get this wrong.

Play it here online.

The Price is Right is a pretty similar show that is still on the air now hosted by Drew Carey. Instead of offering you deals Drew is offering you a chance to guess prices.