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 another solution I think... by mic)

A and D could not be the guilty ones.

To explain, first you must know one of the properties of if-then statements.  If the antecedent is false, then the statement is true.  In other words, the statement "If P, then Q" is true if P is false.  I could say, "If grass is neon orange, then 2+2=2" and I would be saying the truth.  That's just how the system of logic works.

So, since B is innocent, then A is saying the truth, and can't be guilty.

Posted by Tristan on 2004-06-24 18:20:27