Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site rabbit.UUCP
Path: utzoo!linus!decvax!harpo!eagle!alice!rabbit!ark
From: ark@rabbit.UUCP
Newsgroups: net.math,net.rec.bridge,net.misc
Subject: simple (?) statistics puzzle
Message-ID: <1807@rabbit.UUCP>
Date: Tue, 16-Aug-83 15:42:25 EDT
Article-I.D.: rabbit.1807
Posted: Tue Aug 16 15:42:25 1983
Date-Received: Wed, 17-Aug-83 00:32:52 EDT
Organization: Bell Labs, Murray Hill
Lines: 17

A friend gave me this puzzle and mentioned that many people
get it wrong.  I verified his claim -- of the five people I have
asked so far, no one got it right the first try.

I would appreciate solution attempts by mail.  When you send me
your solution, also tell me whether or not you play bridge:
the problem is similar in spirit to some problems routinely faced
by bridge players and I want to see if more of them get it right.

Here goes:  you are in a room with three cabinets, each of which has
two drawers.  One cabinet has a gold coin in each drawer.  Another
has a silver coin in each drawer.  The third has a gold coin in one
drawer and a silver coin in the other.

You pick a cabinet at random and open a random drawer.  It contains
a gold coin.  What is the probability that the other drawer of that
same cabinet contains a gold coin?