in Mathematical Logic retagged by
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6 votes
6 votes

Consider the following popular puzzle.

A boy and a girl are talking. One of them has black hair, another has white hair.
“I am a boy” said the child with black hair.
“I am a girl” said the child with white hair.
At least one of them is lying.

Which of them is lying?

  1. The boy only
  2. The girl only
  3. Both of them
  4. Information is not sufficient to find out the liar
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1 Answer

5 votes
5 votes

$\text{Case 1:}$ Boy has black hair, Girl has white hair :
In this case, no one is lying, But we know at least one of them is lying, So, this case is not possible.

$\text{Case 2:}$ Boy has white hair, Girl has black hair :
Now, both are lying.

So, both are lying.

Detailed Video Solution: https://youtu.be/nclBhBmtz2g?t=2299

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