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A Fourth Person Problem (Posted on 2006-11-01) Difficulty: 2 of 5
We know that Liars always lie about everything, Knights always tell the truth. and Knaves strictly alternate between lying and telling the truth. All the inhabitants of Island T are Knights, Knaves or Liars.

A visiting tourist was busy in conversation with A, B and C who are inhabitants of Island T, when a fourth inhabitant passed them by. It is known that one of A, B, and C is a Knight; the other is a Knave while the remaining one is a Liar. Nothing definite is known about the fourth inhabitant. A, B, and C, say:

A's statements:
1. The fourth person is a Knight like me.
2. Both B and C have been known to speak falsely.
3. C is less truthful than B or myself.

B's statements:
1. The fourth person is a Knave.
2. He (the fourth person) is not like me.

C's statements:
1. If you were to ask the fourth person, he could claim to be a Liar.
2. The fourth person is a Knight.

Out of the first three, who is the Knight, who is the Liar, and who is the Knave? And what is the fourth person?

See The Solution Submitted by K Sengupta    
Rating: 3.1667 (6 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution | Comment 7 of 16 |

I believe A is a knave, B is a Knight, C is a liar and D is a knave.  I belive that A is a knave because it states that C (liar) is less truthful than the Knave and the Knight being that the Knave tells truths and lies whereas the liar just lies.  I say B is a knight because it couldn't be C because it says that the fourth person could claim to be a Liar and it states that the fourth person is a knight.  If a knight tells the truth all the time there is no way that he could claim to be a liar, therefore leaving C as a liar.  I say D is a knave because B (knight) say that it is a Knave and is not like him, which is true.


  Posted by Demplez on 2006-11-03 10:31:38
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