Raymond Smullyan’s “The Island of Questioners” Puzzle


The Island of Questioners

Somewhere in the vast reaches of the ocean, there is a very strange island known as the Island of Questioners. It derives its name from the fact that its inabitants never make statements, they only ask questions. The inhabitants ask only questions answerable by Yes or No. Each inhabitant is one of two types, A and B. Those of type A ask only questions whose correct answer is Yes; those of type B ask only questions whose correct answer is No. For example, an inhabitant of type A could ask, “Does two plus two equal four?” But he could not ask whether two plus two equals five. An inhabitant of type B could not ask whether two plus two equals four, but he could ask whether two plus two equals five.

I once visited this island and met a couple named Ethan and Violet Russell. I heard Ethan ask some, one, “Are Violet and I both of type BY’ What type is Violet?

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