ou are a logician in training for the police, and the time has come to take the certification test. The police chief brings you the test one morning, and says, "I must warn you, this is your only chance at the certification test; If you fail, you must keep training for another year before you can take it again."
           
- Five suspects were interrogated for a bank robbery.
             
- Each suspect was either a knight, a knave, or a liar.
         
- Knights always tell the truth.
       
- Liars always lie.
       
- Knaves strictly alternate truths and lies with each statement.
                   
- Police have evidence that suggests the perpetrator acted alone.
                   
- Police have evidence that suggests the perpetrator acted alone.

>During the interrogation, two questions were asked (consecutively) of each of the five suspects. Each suspect heard the other suspects' responses, and none of them made a statement between his or her two answers. Here are the two questions and their responses.

"Did you rob the bank?"
A: No.
B: No.
C: No.
D: Yes.
E: Yes.

"Who robbed the bank?"
A: E.
B: A.
C: l don't know.
D: E.
E: A.

The interrogators mentioned that something about their statements didn't seem quite right. The police chief adds, "The only hints I can give you are that C is not a knight and that there is only one correct answer. I'll be back in 24 hours to ask you who robbed the bank."

One must assume that the police are always telling the truth - both the uncertain "something" that is not right and the chief.  Thefore, should we place high signficance on the "suggests... acted alone"?  If so, then the key might be that NONE of the suspects could possibly know if the other did it or not - since the perp was "alone".

If you follow that to it's logical conlcusion, then any lie-first knave cannot really know he is telling the truth when he names another as the perp, therfore any solution  that involves a lie-first knave is impossible (except for C).  If one examines each suspect as the possible perp., then only one, C, can be guilty.  All other solutions have a lie-first knave or C as a Knight.

Any disputes? (I welcome them)

Edited on February 16, 2006, 7:54 pm

Posted by Kenny M on 2006-02-16 19:51:34