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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?

- The boy only
- The girl only
- Both of them
- Information is not sufficient to find out the liar

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