Theos-Talk Archives (December 1999 Message tl00238)

Maureen T Fitzgerald wrote:
>
> Hmmm, is that like that riddle I can't quite seem to remember?  That one where
> if you ask that particular person a question he will always tell you a lie, and
> so on and so forth...

	Here's a version of the riddle. You are convicted of a crime in a
country where cleverness is considered to be a redeeming feature.
Instead of being sent straight to jail, you are sent to a room with two
doors. Go through the correct door, you gain your freedom. Go through
the wrong door, you serve your full sentence. In front of the correct
door stands a guard who always tells the truth. In front of the
incorrect door stands a guard who always lies. You may ask a single
question with a "yes/no" answer to either guard, which the guard is
required to answer to the best of his or her ability (meaning that if
you ask a guard, "Have you stopped beating your wife?", and neither
guard is married, the truthful one will say "no", and the liar will say
"yes", since you can't stop without starting). What question do you ask,
and how do you interpret it?

ANSWER:
	You ask, "If I ask the other guard if he guards the door to jail, what
will he say?". If you ask the truthful guard, he will say, "No", since
that is what the liar will say. If you ask the liar, he will say "Yes",
since the truthful guard would say "No". Go through the door of the
truth-teller.

	Bart Lidofsky