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."

Dustin's new post reveals that the "cryptographic" message must indicate something like "KNIGHTS > l". (the word KNIGHTS is missing from the original, as is the > sign) I am assuming that refers to the fact that the number of knights in the lineup is greater than the number of liars.

I reproduce here from AvalonXQ's "insoluble" comment (#11) the only one of the five possibilities he gave that has more knights than liars.

Solution 5:  E did it.  A is a knight, B is a knave (true first), C is a knave (true first), D is a knave (false first), E is a knave (true first).

Possibly the only reason the interrogators thought something was odd about the answers was simply the letter 'l' present in C's answer - since this puzzle is a '2' difficulty, I am thinking all the far-fetched ideas we had about the Chief being a knave or the answers being out of order were just because of the fact that we were working on insufficient information.

If I'm correct, thanks Dustin for the fun puzzle and I'm sorry it was sort of ruined by the fact that it was posted incorrectly.

Edited on March 8, 2006, 10:26 am

Posted by Avin on 2006-03-08 10:24:47