KöMaL 2023 K749
Aladdin found five coins in a box. One of them is a counterfeit coin, and the monkey Abu is the only one who knows which. If Aladdin selects three coins and gives one of them to Abu, then Abu will tell him whether there is a counterfeit one among the other two. Whenever Abu gets a real coin, he will tell the truth, but he will lie if he gets a counterfeit coin. Is it possible to identify the counterfeit coin with at most three questions?
Official text KöMaL. Quoted with source.
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