Home > Logic > Liars and Knights
| The trio (Posted on 2017-08-21) |
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You meet a trio of people, A, B, and C. You know that one of them is a knight, one is a liar, and one is a normal, but you are not sure which is which. Normals tell the truth and lie at random. You are allowed to ask three yes-or-no questions. What three questions can you ask to find out which is which?
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Submitted by Math Man
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Solution:
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First, ask A, "Are you a knight if and only if B is a normal?" If A says, "Yes," then C is not a normal. If A says, "No," then B is not a normal. Then, ask the one that you know is not normal, "Does 1+1=2?" If they say, "Yes," then they are a knight. If they say, "No," then they are a liar. Finally, ask the non-normal, "Is A a normal?" Then, you will know if A is a normal. Then, you will know what the last person is.
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 | solution | Charlie | 2017-08-21 12:23:07 |
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