Puzzle cache

[Johnmelad]

A person is standing at the coordinates of the cache. He/she has a choice of opening one of two doors in order to find the cache and sign the log.

However, each door is guarded by someone - one guard is a liar other one tells the truth.

This person wants to log the cache. What question does he/she have to pose to either of the guardians so that he knows which door the cache is behind? :coffee:

[martybartfast]

Ask either guartdian the question "If I ask the other guardian which door is the cache behind, what will he say?" whatever answer you get is the wrong one, so choose the other door.

[keehotee]

...assuming the liar always lies.....

[Mrs Blorenge]

I've been trying to visualise this scenario in its various permutations...

Now my brain hurts.

Back to bopping that stupid ball on a string...

[martybartfast]

A always lies, B always tells the truth.

X is the correct door, Y is the wrong door.

If you ask A what will B say, he knows that B would tell you the correct door - X, but A will lie and therefore tell you that B would say Y.

If you ask B what will A say, he knows that X is the correct door but he knows that A will lie to you so B will tell you that A will say Y.

In either case you will be told the wrong door.

[keehotee]

A always lies, B always tells the truth.

X is the correct door, Y is the wrong door.

If you ask A what will B say, he knows that B would tell you the correct door - X, but A will lie and therefore tell you that B would say Y.

But he's a liar, and not to be trusted.
What grounds do you have to assume he always lies ....??h34r:

[martybartfast]

But he's a liar, and not to be trusted.
What grounds do you have to assume he always lies ....??h34r:

Well if when you ask both guards you get a definite answer then you know that the liar always lies, because the truthfull one knows what the liars answer will be, if on the other hand the liar only lies some of the time then the truthful one will honestly answer "I don't know" (because he can't know whether the other one will choose to lie or not), in this case all you can do it take pot luck.

[Team Vorvik]

Erm..... ennie meanie minnie moe out you go..... it must therefore be the first door... JMHO it always works for me...