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Knights, Liars, and Spies III (Posted on 2022-03-07) Difficulty: 3 of 5
On a remote, mysterious island there are three kinds of people: Knights, who always tell the truth; Liars, who always lie and Spies, who may answer in any order that they see fit.

Riley, who is visiting the island has come face to face with 3 people. One of them wears blue, one wears red and one wears green. Riley knows that one of them is a knight, one is a liar and the remaining one a spy. He inquires who amongst the three individuals is a spy. They respond as follows:
  • The man wearing blue says, "That man in red is the spy."
  • The man wearing red says, "No, the man in green is the spy."
  • The man wearing green says, "No, the man in red is in fact the spy."
Of the three island dwellers, identify the knight, the liar, and the spy, providing valid reasoning.

See The Solution Submitted by K Sengupta    
Rating: 4.0000 (1 votes)

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Solution Solution | Comment 1 of 2
Among the three statements, we have two possibilities - either 2 statements are true and one is false, or else 2 are lies and the third is true. Since we know one of the statements is true, the spy must be wearing either red or green.

If the spy is wearing red, that means that either the man in green or the man in blue is a liar. However, as both identify the spy as the man in red, both would be telling the truth, leading to a contradiction.

Therefore, the spy must be the man in green. This means the man in red is the knight, and the man in blue is the liar. 

  Posted by H M on 2022-03-07 09:10:00
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