246: Labyrinth Puzzle

Explain xkcd: It's 'cause you're dumb.
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Revision as of 00:06, 4 January 2013

Labryinth Puzzle
And the whole setup is just a trap to capture escaping logicians. None of the doors actually lead out
Title text: And the whole setup is just a trap to capture escaping logicians. None of the doors actually lead out


This comic alludes to a famous Knights and Knaves-type logic puzzle, in which there are two doors and two guards. One guard always lies, and the other always tells the truth. One of the doors leads to freedom, and you can only ask one guard one question. The solution to this riddle involves a very tricky question indeed, and one would in the xkcd-version risk a stabbing from the third guard. If you want to give the original puzzle a try for yourself, don't read the spoiling next paragraph.

Solution: Ask one guard (it doesn't matter which one) which door the other guard would say leads out. The door indicated doesn't lead out.


Black Hat: And here we have the labrinth guards. One always lies, one always tells the truth, and one stabs people who ask tricky questions.
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Just ask which color is the sky.. ‎ (talk) (please sign your comments with ~~~~)

Oh, although the strip doesn't explicitly say so; in those riddles you can normally only ask one question. --St.nerol (talk) 23:00, 27 January 2013 (UTC)
There's another (more traditional) three-guard variation where one guard always tells the truth, one guard always tells a lie and the third alternates between pure truth and pure lie (and you don't know which flip they're currently flopped upon). But you still only get to ask one question of one guard. Have fun with that one. My personal solution certainly has a degree of convolution, but I've heard other workable answers. 02:24, 21 June 2013 (UTC)
@‎, you would know which one lies but you would not know which door leads out. Tharkon (talk) 23:13, 10 October 2013 (UTC)
Eh, well, even if you had a perfect question to ask in this case, a lot of good would that do you: it'd only reveal the truth behind the setup, that none of the doors lead out. :p -- 08:20, 8 November 2013 (UTC)
Well yes it says that in the title-text. But good pick-up. 02:31, 6 February 2014 (UTC)

One question, of one guard. I really like the original form of this riddle. It's a bit of a trick, though. It is crucial that the guards "know" each other's rules, but this is not even implied. And if it was stated in the question, that would probably be a good enough clue to get you to the answer. Of course, once you know the answer it seems trivial, but I wonder what percentage of people actually worked it out for themselves? Another good one is Monty Hall, even though that is pure, straightforward probability. 18:11, 17 January 2014 (UTC)

I think somebody needs a hug! 18:11, 17 January 2014 (UTC)
The whole problem with this entire riddle is that if they are both liars you are screwed! Nothing in the riddle establishes a fact that they aren't liars. Now if there was a known truth teller in the riddle that explains the nature of the guards or the narrator does it, then the above solution works. (talk) (please sign your comments with ~~~~)
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