Are you making this up?: The Wknd Puzzle by Dilip D’Souza

Updated on Sep 24, 2022 06:57 PM IST

This week, a a variation on the classic liar / truth-teller conundrum, inspired by the great logician and polymath Raymond Smullyan.

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ByDilip D’Souza

For my final puzzle in this space, a variation on the classic liar / truth-teller conundrums. This is inspired by the great Raymond Smullyan, logician and polymath extraordinaire.

So: hiking in the Western Ghats one rainy morning, you run into a visitor from the mythical country of Yudhinocchio. You know three things about the citizens. First, the population there is made up entirely of sets of identical twins. Second, of each set of twins, one always lies, the other always tells the truth. Third, the liars all have names starting with one letter, truthers all have names starting with another. The letters are Y and N, but you don’t know which is for which.

There’s one more thing about Yudhinocchians: you can only ask them a single three-word question, to which they will answer either “Yes” or “No”.

Question 1: What question can you ask to find out whether her name begins with N or Y?

Or, Question 2: What question can you ask to find out whether it’s Ns or Ys who tell the truth?

Scroll down for the answers.

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Answer 1: Are Ns truthful?

If she says yes, she’s an N. If no, she’s a Y.

Answer 2: Are you an N?

If yes, Ns tell the truth and Ys lie. If no, Ys tell the truth and Ns lie.

I’ll leave you to work out the logic, and then offer a salaam to Smullyan.

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