Three boxes—A, B, and C—sit on a table. One box contains a diamond, and the other two are empty. Box A's label reads: 'The diamond is in Box B.' Box B's label reads: 'The diamond is not in this box.' Box C's label reads: 'Box A is empty.' If exactly one label is true, which box contains the diamond?
Box A.
If the diamond is in Box A: Label A is false, Label B is true ('not in B'), and Label C is false ('Box A is empty' is false because it has the diamond). This leaves exactly 1 true label (B). If the diamond were in B or C, it would produce 2 true labels.
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: Hard. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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