A detective interrogates three suspects in a robbery. Al says, 'Bob did it and Carl is innocent.' Bob says, 'If Al is guilty, then Carl is guilty.' Carl says, 'I am innocent, but at least one of the other two is guilty.' If all statements made by innocent people are true, and all statements made by the guilty person are false, who committed the robbery?
Bob
Test Bob as guilty (false statements): Bob says 'If Al is guilty, then Carl is guilty.' If Bob is guilty, this implication could be false (Al is guilty, Carl is innocent). Al (innocent) says 'Bob did it and Carl is innocent' (True, fits Bob guilty, Carl innocent). Carl (innocent) says 'I am innocent, but at least one is guilty' (True). Thus, Bob is the guilty party.
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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