Three guards stand before a fortress gate. One always tells the truth, one always lies, and one alternates between truth and lies. You can ask one yes/no question to each guard in any order. What is the minimum number of guards you must question to guarantee identifying the liar?
2 guards
By questioning any two guards, you can use logical elimination. If you question the truth-teller and the alternator, or the liar and the alternator, the contrasting answers allow you to pinpoint the liar based on their behavioral rules.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Medium. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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