wu :: forums - Print Page


    
      
        wu :: forums
        (http://www.ocf.berkeley.edu/~wwu/cgi-bin/yabb/YaBB.cgi)
      

        riddles >> easy >> Three Supercomputers, One Question
        
(Message started by: FiBsTeR on Mar 14^th, 2009, 6:18pm)

Title: Three Supercomputers, One Question
Post by FiBsTeR on Mar 14^th, 2009, 6:18pm

A variation of a well-known puzzle, though I'm not sure if this has a solution (I'm not sure of the source). If you find one, please hide it. I just want confirmation that an answer exists; I don't want to lose any more sleep over a problem with no solution. ;)

=====

There are three supercomputers that output (in English) answers to yes/no questions. One always tells the truth, one always lies, and one outputs randomly. They are indistinguishable in appearance. You can pose one question to any computer. Can you find a computer that is not the one that always lies?

You can assume that only questions that will output answers in all cases can be asked. For example, you can't ask "Will you answer no?" because the truth computer would blow up.

EDIT: I am aware that one can find a non-random computer in one question.

Title: Re: Three Supercomputers, One Question
Post by Grimbal on Mar 15^th, 2009, 2:01am

I think it is not possible.

[hide]
If you ask your question to Liar, it will reply yes or no. Your decision for that reply must be to pick another computer as non-Liar.

Random can reply the same as Liar would have done. And Random replies regardless of who is who. So for the same reply you can not exclude any other computer from being Liar.

So if you get an answer consistent with Liar's reply, you can not exclude any computer from being Liar.
[/hide]

Title: Re: Three Supercomputers, One Question
Post by FiBsTeR on Mar 15^th, 2009, 5:26am

Oh wonderful, thank you. I've been toying around with an argument like that but I could never really convince myself. ;D

Title: Re: Three Supercomputers, One Question
Post by mistaken_id on Mar 15^th, 2009, 7:49am

Quote:

EDIT: I am aware that one can find a non-random computer in one question.

How ???

Title: Re: Three Supercomputers, One Question
Post by Grimbal on Mar 15^th, 2009, 3:42pm

Let's call the computers A, B and C.
Ask to A: "Is B always lying or C always telling the truth?".
If yes, pick B. If no, pick C.

Title: Re: Three Supercomputers, One Question
Post by FiBsTeR on Mar 15^th, 2009, 3:52pm

Or also:

"If I asked you yesterday if B is random, what would you have said?"