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Try to solve this one:

You are at an unmarked intersection ... one way is the City of Lies and another way is the City of Truth.
Citizens of the City of Lies always lie.

Citizens of the City of Truth always tell the truth.

A citizen of one of those cities (you don't know which) is at the intersection. What question could you ask to them to find the way to the City of Truth?

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I would ask the person

which way leads to your city?

Since

Both the liar and truth teller would point to the way to the City of truth.

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  • $\begingroup$ "Back the way you came." "Straight up into the sky." This is why it's wise to stick to yes-or-no questions in those parts, like "Does that road lead to your home city?" $\endgroup$
    – aschepler
    Jul 25 '20 at 16:53
  • $\begingroup$ @aschepler Good point. However, if the person was this evasive (such as a politician), yes-or-no questions might be of no help either. $\endgroup$
    – A.O.
    Jul 25 '20 at 18:19
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Ask the citizen:

Where would the citizens from the other city tell me the City of Lies is?

That way, either if the citizen is a liar, or an honest person, both will point to the City of Truth.

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Here is another solution:

If I ask you which way is the City of Truth, which way will you point at?

Explanation:

If the citizen being asked happens to be a liar, "which way is the City of Truth" will make the citizen point to the City of Lies. But adding "If I ask you", the citizen will need to lie about where the citizen will point to, thus the 2 lies will give us the correct answer.

If the citizen being asked happens to be honest, well, that's great!

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