Professor Z was killed by one of his four students, who was helped by another of the four. His students declared:

A: If B is guilty of something, then C must be innocent.
B: If A is innocent, then C must be guilty.
C: If B was the killer, then D must have had nothing to do with the crime.
D: I am innocent.

As everybody should know, guilty parties always lie, and innocent people always tell the truth. Who killed the professor, and who was his accomplice?

(In reply to if d is not the killer... by Chandrakant)

A can't be the killer. Neither can C. This can be seen instantly because their statements starts with "If x is guilty." If A or C were guilty, then this first part of the conditional would be false, so the entire conditional would be true, so they would be telling the truth. Since guilty people can't tell the truth, they can't be guilty.

Posted by Sam on 2004-03-06 13:27:11