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Path: utzoo!linus!decvax!tektronix!richl
From: richl@tektronix.UUCP (Rick Lindsley)
Newsgroups: net.math,net.misc,net.rec.bridge
Subject: Re: simple (?) statistics problem solved
Message-ID: <1287@tektronix.UUCP>
Date: Thu, 25-Aug-83 01:02:02 EDT
Article-I.D.: tektroni.1287
Posted: Thu Aug 25 01:02:02 1983
Date-Received: Fri, 19-Aug-83 12:57:07 EDT
References: <1814@rabbit.UUCP>
Organization: Tektronix, Beaverton OR
Lines: 21

Hold it! 2/3 is the probability that given the constraint that
you have ordered pairs of coins you will choose one that has at
least one gold coin. Your argument is only valid if you are not
allowed to update your information to apply to the situation.

The key to the argument is whether you calculate the probability
BEFORE you see the gold coin or after. If before, then your reasoning
may hold, but if you calculate the probability with the knowledge that
I hold in my hand a gold coin and I have just chosen the first of
ordered pairs (S,S) (G,S) or (G,G), then I can eliminate the first
ordered pair from my calculations. It is not in the set of possibilities.
I then have two possiblities remaining, and one of them is desirable.

Put another way, if you put me in the above described situation,
with one gold coin in hand and one drawer left to open, I can assure
you that I would be correct 50% of the time by just saying, "Yep,
the other one must be gold".

Rick Lindsley
richl@tektronix
...tektronix!richl