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.

Some notation: knights, liars, and someone we know did not steal the wallet.

Dwayne says that Allan is a liar, so they cannot both be knights.
A B C D E F

Calvin says that they [Allan and Dwayne] are [liars], so he is a liar. From this, Eddy did not steal it.
A B C D E F

Eddy says that he did not steal it, so he is a knight.
Therefore, Calvin did not steal it.
Also, there are only four knights.
A B C D E F

Barry also says Calvin is a liar, therefore he (Barry) is telling the truth.
From that, then, we know that he did not steal it and Allan also did not.
A B C D E F

Fred says that Barry did not steal it, so Fred must be a knight.
A B C D E F

If Fred is telling the truth, then Allan is a liar, and Fred did not steal it.
A B C D E F

Since Dwayne says (truthfully) that Allan is a liar, he is a knight.
Therefore, Dwayne is also telling the truth when he says that he did not steal it.
A B C D E F

So, none of the six stole the wallet?
The knights are Barry, Dwayne, Eddy, and Fred, while Allan and Calvin are lying.

Perhaps you (the author) are a liar, your wallet is not really missing, nobody stole it, you really can figure out if they are truthtellers, and you never asked a few questions anyway, you liar. You're not even sure that all the men are either knights or liars.

Posted by DJ on 2003-06-10 14:14:56