A Riddle with a Logical Solution

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After all this talk of the Sally Anne test here is something which equally does your head in although it should (in theory) be more accesable to us as it is based on logic.

The Riddle:

There are two doors. One leads to certain death and the other to a hoard of treasure.

Each door is guarded by a soldier. One always tells the truth and the other always tells lies.

You must choose a door and walk through it.

You can only ask one guard one question before you must choose.

What question do you ask?

Does the honest guard guard the treasure door, and the lying guard guard the death door?

Or, do you know which guard is which?

If so, i may have the answer...

This isn't the question, i'm just wondering about the riddle...

What... is your favorite color?

What... is the airspeed velocity of an unladen swallow?

And to answer the first riddle: Would he tell me that this is the door that leads to the castle, I mean, treasure.

Only the guards know who guards which door and whether their colleague tells the truth or lies.

elaborate

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Last edited by Ante on 09 Nov 2005, 5:02 pm, edited 1 time in total.

I would guess that the doors are and do just what we expect. The treasured door is honest, and the death door lies.

I will put my sister in the room naked, and if either soldier looks at her, then i'll know.

[quote="another brain teaser"]
The Riddle:

There are two doors. One leads to certain death
and the other to a hoard of treasure.

Each door is guarded by a soldier. One always tells
the truth and the other always tells lies.

You must choose a door and walk through it.

You can only ask one guard one question before
you must choose.

What question do you ask?

Is the treasure in their because the liar would
say yes and the truthful one would say
No! You can argue that the liar would say
no, but the truth was no to his door and he
is a "liar"

Hmmmmm?
This is my stab at it!

Sincerely,
Ghosthunter

You pick one of the doors (we'll call this door A), and ask that guard: "What would the other guard say if I asked him if the treasure was behind his door?"

If the guard says "Yes", then you enter door A. If the guard says "no", then you enter the other door (B).

Let's look how this would play out:

1) If the treasure is behind door A:
a) Guard A is the liar: Guard B would say "no", so guard A says "yes"
b) Guard A is the truthteller: Guard B would say "yes", so guard A says "yes"

2) If the treasure is behind door B:
a) Guard A is the liar: Guard B would say "yes", so guard A says "no"
b) Guard A is the truthteller: Guard B would say "no", so guard A says "no"

Hope you can follow that - took me a while to get it all figured out! I kept going around in circles and messing myself up!

Thats it.

I have always found this riddle fascinating and each time I try to explain it to someone I have to think it through really carefully ~ it does send your head around in circles.

I think it is fascinating because it is a logic based problem but in order to think it through you have to try and imagine a guard imagining what the other guard would say.

I find that difficult. It is a bit like imagining what Sally imagines Anne is thinking in the Sally Anne test.

Even though I know the answer to this riddle it still does my head in.

I'm going to have a lie down now.

Brilliant! I didn't get it.

But, just to be nit-picky -- the riddle should specify that the guards know what's behind the doors -- or at least behind their own door. I assumed that, but another Aspie here didn't ('cause he took the text literally, as he always does!).

That is a clever riddle.

GoneFission's answer was exceptionally clever...

My answer to the riddle is a little less involved. I'd simply ask either guard "Are you a guard?". The one who says yes will show you the money

You could be even more annoying and ask one guard "Is the pope Catholic?" or "Do bears *** in the woods?" or any question that has a definite wrong or right answer.

Am I the only other one in here who has seen the movie Labrynth???