Ask Marilyn

In the Sunday issue of the Dallas Morning news, there's a magazine called Parade. Ever since I was a kid, I've read a column in Parade called "Ask Marilyn," in which the woman with the reportedly world's-highest I.Q. answers questions ranging from word puzzles to politics.

Here's one math puzzle that I recently came across.

Suppose you are on a game show. There are three closed doors,

A ----- B ----- C

and the host tells you that behind two of the doors are two goats, and behind one of the doors is a brand new Porsche. If you select the door hiding the Porsche, you leave with the car. If you pick one of the other two doors, you get a goat. You are told to pick a door, which you do. Let's say you pick A.

A ----- B ----- C

Instead of opening the door, the game show host, knowing where the Porsche is, opens one of the doors you did not select to reveal a goat.

A ---- goat---- C

or

A ---- B --- goat

He then tells you that you can either stay with the door you originally picked (A), or you could switch your selection to the other door which remains closed.

Unfortunately you've already used your "eliminate an answer" lifeline. Your Aunt Nelda, the math teacher, is away from her phone. (Another lifeline burned.) Your last lifeline, the audience poll, shows :50% say to stay with the door A, 49% say to switch doors, and 1% say, "If you randomly pick a shirt and tie from your closet, what's the chance that their colors would exactly match?"

What do you do, and why? I'll post Marilyn's answer on Thursday.