Brainteaser #18 – Knights and Jokers

brainteasers

“Raise the castle gates!”

3 men walk into the castle courtyard. Your reconnaissance has informed you that one is a spy, another is a joker that never tells the truth, and that the final person is an honourable and truthful knight. You do not know who is who.

They wear red, blue, and green.

The blue man declares firstly “I am not a spy!”

The red man says “I am the joker!”

The green man says “If you were to ask me, I would say the red man is a spy!”

How do you find the true identities of these men?

Show Answer

The red man declares he is the joker, but we know this cannot be true, as the joker never tells the truth. This also means he cannot be the knight, as the knight would indeed say he is the knight.

This means the man in red is the spy. 

Since we know the man in red is a spy, we know the blue man is telling the truth.

The blue man must, therefore, be the knight. 

This leaves the man in green as the joker. Even though the red man is the spy, the green man always lies. He declared the red man was a spy, meaning he lied, which verifies his identity as the joker

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