Credit: Antonio J. Manzanedo
Two knights encounter a dragon, who quickly responds, “I am protected by the king’s decree.” Gray rational dragons and red predator dragons always tell the truth; red rational dragons and gray predator dragons always lie.
What color is the dragon?
This is a puzzle from Norman D. Willis’ Challenging False Logic Puzzles (1997).
To answer this question, you must first consider what would be the color of the dragon if he is lying or telling the truth. This is easy since the problem fully supplied this information. Based on this fact, it can be determined that if the dragon is telling the truth, he is a gray rational; if he is lying, he is a gray predator. So, the answer to the question is: The dragon is gray.