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Question

A liar always lies and a non-liar, never. If in a group of $n$ persons seated around a round-table everyone calls his/her left neighbor a liar, then

The correct answer is
$n$ must be even and every alternate person is a liar

To solve the problem, we need to analyze the situation where every person seated around a round table calls their left neighbor a liar. We have to identify the condition in terms of the number of people, \(n\), such that the statements hold true.

Let's consider the implications of the statements:

  1. If a person calls their left neighbor a liar and is telling the truth, then their left neighbor must indeed be a liar.
  2. If a person calls their left neighbor a liar and is lying, then their left neighbor must be a truth-teller, as they cannot both be lying about the same thing.

Given the setup, this establishes a pattern: person A calls person B (to their left) a liar, which implies the following sequence:

  • Person A = Truth-teller, Person B = Liar
  • Person B = Liar, Person C = Truth-teller

This alternating pattern must continue around the circle. For this arrangement to be consistent in a full circle:

  • There must be an even number of people (\(n\) is even), so the cycle can repeat exactly.
  • This pattern will result in every alternate person being a liar.

Now, let's evaluate the options:

  • All are liars: This is impossible because, in such a case, each person would be lying about their left neighbor, which would create a contradiction.
  • \(n\) must be even and every alternate person is a liar: This is consistent with our analysis.
  • \(n\) must be odd and every alternate person is a liar: This would not complete the alternate pattern accurately.
  • \(n\) must be a prime: Prime numbers do not determine the pattern of liars; rather, it is parity (odd/even) that determines consistent results.

Therefore, the correct answer is: \(n\) must be even and every alternate person is a liar.

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Important Questions from Puzzle (Notes)

  1. Seven boxes S, F, G, H, T and U are kept one over the other but not necessarily in the same order. Only two boxes are kept below S. Only one box is kept above U. Only one box is kept between U and B. G is kept immediately above F. T is kept at some place below H.
    How many boxes are kept between H and G?
  2. Seven boxes E, F, G, H, S, T and U are kept one over the other but not necessarily in the same order. H is kept immediately above E. T is kept immediately above U. Only F is kept above S. Only two boxes are kept above H. T is not kept at third position from the bottom.
    How many boxes are kept between G and F?
  3. Seven boxes E, F, G, H, S, T and U are kept one over the other but not necessarily in the same order. Only H is kept above E. Only T is kept between E and S. Only F is kept below U.
    How many boxes are kept between G and F?
  4. Seven boxes E, F, G, H, S, T and U are kept one over the other but not necessarily in the same order. Only four boxes are kept between H and E. Only S is kept above H. Only two boxes are kept between F and U. T is kept immediately above G. U is not kept immediately above T. Which box is kept fourth from the top?

  5. Seven boxes E, F, G, H, S, T and U are kept one over the other but not necessarily in the same order. Only H is kept above E. Only T is kept between E and S. Only F is kept below U.
    How many boxes are kept between G and F?
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