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 I don't know. (Posted on 2006-02-16)
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."

 No Solution Yet Submitted by Dustin Rating: 3.3333 (6 votes)

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 Missing something. . . or am I? | Comment 1 of 52

I think I am missing something.  I can only solve this if I assume that there is at least one knight, one knave and one liar. In which case I nominate A as the criminal.

Or if I am looking too hard.  Assume C's 2nd statement is the truth. Then since she is not a knight, C's first statement is a lie (alternating) and C robbed the bank. At this point C's 2nd statement must be a lie. In which case C know's the robber, but if the robber acted alone the C must be the robber.

Difficulty two.  Hmmm . . . lots of red herrings.

 Posted by Leming on 2006-02-16 14:40:49

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