A master locksmith has three identical-looking brass keys that open three different doors: the Archive, the Vault, and the Study. Each key opens only one specific door. If the locksmith tests a key on the Archive door and it fails, what is the maximum number of additional trials needed to ensure every key is correctly matched to its door?
0 trials
Logic dictates that if you test one key and it fails on the Archive, you try it on the Vault. If it fails there too, it must belong to the Study. Furthermore, by process of elimination, the remaining two keys and doors are automatically solved in your hand without needing any further physical trials.
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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