Very tough riddle

[korzon]

There are three brothers (They know each other). One always tells the truth, one always lies, and one gives random answers. You need to figure out which is which by asking any of them a total of three Yes/No questions. You can't ask questions that can't be answered with certainty (IE: "Would your brother tell you the truth if you ask him a question?" is invalid because if the brother you are referring to gives random answers then he will not know the answer).

Good luck!

 

[c39b7]

Ask each brother the same question twice: Which direction is up?

hehhehe

 

[fryman04]

What's so difficult? Just show them a yellow paper and ask "is this paper yello?".

 

[c39b7]

Yes, it can be any question of that simplicity, but you must ask more than once to each brother, to compensate for the fact that brother 3 gives random answers; so there is a chance that both he and the truthful brother will give the same correct answer.

 

[korzon]

If you ask each brother "Is the sky blue" you will either
"Yes", "Yes" and a "No"
Or "No", "No" and a "Yes"

This will either unveil the lier or the truth teller respectively, but you will not be able to differentiate between the other two.

So, with 4 questions, you can do it trivially. Only having 3 questions is what makes this riddle extremely dificult.

Took me many hours to solve it.

 

[Honan]

There are three brothers (They know each other). One always tells the truth, one always lies, and one gives random answers. You need to figure out which is which by asking any of them a total of three Yes/No questions. You can't ask questions that can't be answered with certainty (IE: "Would your brother tell you the truth if you ask him a question?" is invalid because if the brother you are referring to gives random answers then he will not know the answer).

Good luck!

http://rinkworks.com/brainfood/s/wd.39.shtml