🚀 go-pugleaf

In article <1993Jan26.143630.1@skaro.demon.co.uk> richard@skaro.demon.co.uk (Richard Develyn) writes:
>
>You and two other people (call them B and C) are locked, in separate 
>cells, in a prison.  You are told that two of you are to be executed. 
>So you calculate your chances of survival to be 1 in 3.
>
>The gaoler wanders round and you say to him that, since clearly at 
>least one of the two other chaps is going to die, he wouldn't be 
>giving anything away by telling you which one. He does - say B. Now, 
>amazingly, you calculate your chances of survival as 1 in 2 since it 
>is clear that either C or you will be the other victim.

Aaargh--it's Monty Hall all over again.

Cajoling the gaoler into giving you information about the other
prisoners doesn't tell you anything about yourself in this case.
Your odds of survival are still 1/3.  The odds of C's survival
(based on what you now know) have risen to 2/3, however.

So if the warden comes around and says he will not tell you who
is to be executed but he will let you change places with one of
the other prisoners if you like (and so to suffer whatever fate
had been decided for them), it is to your advantage to take
C's place.

-- David Karr (karr@cs.cornell.edu)