You meet six men on a road side. The problem is that your wallet is mysteriously missing and you can't figure out if these men are truth tellers or not. So you ask a few questions and here are their answers:

Allan: "Fred stole it. Fred also hears quite well."

Barry: "Calvin is a liar. I did not steal it and I know Allan did not steal it."

Calvin: "Allan and Dwayne are both knights. Eddy stole it."

Dwayne: "Allan is a liar. I did not steal it."

Eddy: "Only 4 of us are knights. I did not steal it. I know Calvin did not steal it."

Fred: "I am deaf but read lips. Barry did not steal it."

Who stole the wallet?

P.S. You are sure that all of the men either lie or tell the truth. No one does both.

Walking the tree of posibility

Assume Allan speads truth:
Implies Fred is thief and Fred lies
When fred lies, it means that barry is the thief. There is only one thief, so Allan lies!

Allan lies:
Fred is not thief and fred speaks the truth
Fred speaks thruth = Barry is not thief
Barry is not thief, so barry speaks the truth
Barry speaks truth = Allan is not thief and Calvin lies
Calvin lies = Eddie is not thief
Dwayne: "Allan is a liar" which is true as we have seen, so dwayne speaks truth
dwayne speaks truth = Dwayne is not thief
Now we have : Fred, Barry, Allan, Eddie, Dwayne are not thief
So Calvin is the thief

Posted by rob on 2003-06-12 05:05:47