In the "1 man lies and the other tells the truth" riddle, couldn't you just ask one a simple math question?

IE, a question YOU know the answer to??

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lemonie6 years ago
Yes you could, that's a good piece of logic.
However, in the riddle you need to find out the answer to a question which isn't math'. If you had two questions it would work, but you only get one.

The answer is a simple binary / boolean:
If person A outputs FALSE where it should be TRUE and person B outputs TRUE for TRUE, you ask "what would the other person answer to this question?" It assumes that persons A and B know each other and their logical-operation. But the outcomes are :

A would say (TRUE but I do FALSE for TRUE so- ) I say FALSE" or B (I know B will say FALSE so- ) FALSE. You get the same TRUE answer regardless of which person you ask. It works the by logically cancelling out a common uncertainty factor or something like that...

L

Why couldn't you ask them what 2+2 is? The liar would give an incorrect answer and the truthful man would say "4."

ajleece (author)  lemonie6 years ago
I do know the answer, but I'm not 100% on the specific rules of the question.

But if you're allowed to ask ANY question, shouldn't a question you know the answer work too?

However, if you may only ask a true false question, yes, there is only one answer.
lemonie ajleece6 years ago
Asking ANY question will get you an answer. It isn't necessarily the answer you need, like "Which cake should I eat?"
You only get the one question.

L
ajleece (author)  lemonie6 years ago
But you could ask "Are you a Male" or "What colour is the sky" or "2+2" or "Can you hear me"

All of those questions will give you an answer which you could use. IE, if you know the person is male, and they say they are not, then you know they're the liar.
lemonie ajleece6 years ago
Yes, but which cake do you eat, which box do you open, what colour door do you step through?
It doesn't matter which one tells the truth if you only get the one question. It's logic, not a conversation.

L
ajleece (author)  lemonie6 years ago
We must be working with different problems, but I get what you mean.
Yes, it would work because you would easily be able to identify the liar, however, in most versions of this question you are only allowed to ask a single question. Which means you can easily identify the liar but you never asked about the two cities (or whatever the riddle is about), therefore you do not get a useful answer.

That being said, if you have 2 questions, that is an easy solution.
aelias366 years ago
Or ask if they're men.
ajleece (author)  aelias366 years ago
Assuming they're not women. :p
Re-design6 years ago
I think one of the guidelines is that you don't cheat and ask a question that you know the answer to.
ajleece (author)  Re-design6 years ago
You can't 'cheat' if you don't get given any guidelines.