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Path: utzoo!linus!decvax!duke!unc!mcnc!idis!mi-cec!dvk
From: dvk@mi-cec.UUCP (Dan Klein)
Newsgroups: net.math
Subject: Let's Make a Deal
Message-ID: <165@mi-cec.UUCP>
Date: Mon, 3-Oct-83 09:48:23 EDT
Article-I.D.: mi-cec.165
Posted: Mon Oct  3 09:48:23 1983
Date-Received: Tue, 4-Oct-83 01:15:41 EDT
Lines: 13

Scott-
	Sorry.  While your math is correct, your assumptions are wrong.
Indeed, the probability of any door being the winner is 1/3.  Having ruled
out the door Monty shows you gives a 2/3 probability of *either* of the
two remaining doors as being the good one (WRT the set of three).  Given that
the probability of *any* door being good as 1/3, you seeing a bad door does
not change the probability of either remaining door being good.  Once you know
that door #1 is bad, the probability of doors #2 & #3 being good (or bad) is
now 1/2.  It don't make no nevermind what you do!  Stay or change, your chances
are the same, and you'll look just as foolish when he shows you the cow and
milking stool whether you changed or not.

			-Dan Klein, Mellon Institute, Pittsburgh