On Fri, 13 May 2011 12:19:45 -0700, "Bill Graham"
wrote:

Arny Krueger wrote:
"Bill Graham" wrote in message

Soundhaspriority wrote:
"Suppose you're on a game show, and you're given the
choice of three doors: Behind one door is a car; behind
the others, goats. You pick a door, say No. 1, and the
host, who knows what's behind the doors, opens another
door, say No. 3, which has a goat. He then says to you,
"Do you want to pick door No. 2?" Is it to your
advantage to switch your choice?" The above is a famous problem.
I've left out the
attribution to give you a few minutes (or forever, if
you want) to enjoy it. Bob Morein
(310) 237-6511

When you pick door #1 you only have a 1/3 chance of
winning. But after you see that there is a goat behind
door #3, your chance of winning is 1/2, so I would change
doors and pick door #2. But I don't really know
why....It's just gambler's instinct with me.

After you know there is a goat behind door #3 and are given a chance
to guess again, there is a 50% chance the car is behind door #1 and a
50% chance the car if behind door #2. Change your choice or not, you
have a 50% chance of being right.

But when you first entered the arena, you only had a 1/3 chance of winning.
How does that chance change halfway through the game, and why would it
matter whether you changed doors or not?
Exactly!!! In effect it is a new game. You can choose the same door,
or you can choose the other door. The car is behind one of them.
50-50.

PlainBill