[Guest]

There are three persons, John, Peter and his wife Sarah. One of them always lies, the other is always honest. The third always tells the truth after a lie, and lies after telling a truth; however, the credibility of that person's first answer is unknown.

Taking into consideration that you have three questions to ask, each to one person of them, and that you can ask the same person more than one question, what questions should you ask, and to whom, if you want to know who is who?

Edited April 18, 2009 by HellFire

[Guest]

There are three persons, John, Peter and his wife Sarah. One of them always lies, the other is always honest. The third always tells the truth after a lie, and lies after telling a truth; however, the credibility of that person's first answer is unknown.

Taking into consideration that you have three questions to ask, each to one person of them, and that you can ask the same person more than one question, what questions should you ask, and to whom, if you want to know who is who?

Ask Peter," Is your wife Sarah?"

Ask Peter," Is your wife Sarah?"

Ask Sarah," Is your husband Peter?"

[plasmid]

Do they have to be strictly yes/no, or some other form where there are only two possible answers?

[Guest]

Ask Peter," Is your wife Sarah?"

Ask Peter," Is your wife Sarah?"

Ask Sarah," Is your husband Peter?"

What if Peter was the honest one, and Sarah answered no, then u can't know if Sarah is a liar or the unreliable one.

Do they have to be strictly yes/no, or some other form where there are only two possible answers?

yes/no

Edited April 18, 2009 by HellFire

[Guest]

This is an old puzzle found in many different variations on the net: "3 gods", "Truthteller/liar/random", etc.

It was posted in BrainDen by Martini 2½ years ago - hence I believe this thread will be closed soon.

The liar, the truth tellar...: http://brainden.com/forum/index.php?showtopic=373