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From: dap1@ihlpf.UUCP
Newsgroups: net.math
Subject: "Prisoners - (nf)"
Message-ID: <191@ihlpf.UUCP>
Date: Sat, 27-Aug-83 19:00:59 EDT
Article-I.D.: ihlpf.191
Posted: Sat Aug 27 19:00:59 1983
Date-Received: Tue, 30-Aug-83 11:56:55 EDT
Organization: BTL Naperville, IL
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#N:ihlpf:6200013:  0:1005
ihlpf!dap1    Aug 27 17:32:00 1983

Here's a variation on a problem I heard long ago (I don't recall where):

A judge sentanced three men and placed them in cells.  The stipulations
of the sentance were that at the end of the week, the judge would pull
one prisoner's name from a hat and that prisoner would be executed.  The
other two would be set free.  The prisoner in the third cell reasons as
follows:

Only one of us will die, so either the prisoner in cell A will live or
the prisoner in cell B will live.  Suppose the prisoner in cell A will
live.  Then I have a 1/2 chance of death.  On the other hand, suppose the
prisoner in cell B will live.  I still only have a 1/2 chance of living.
Thus, in either of these cases, I only have a 1/2 chance of living!

It's not TOO hard to figure out where his reasoning went wrong, but it makes
for an interesting question for those unacquainted with probability.

                                                     Darrell Plank
                                                     8/27/83