A boy and a girl are sitting on a bench.
“I am a boy,” says the child with black hair.
“I am a girl,” says the child with brown hair.
At least one of them is lying. Who is the boy and who is the girl?
Answer
They are both lying.
Scenario 1: If the child with black hair is lying, she is a girl. Then the child with brown hair cannot be a girl and is also lying.
Scenario 2: If the child with brown hair is lying, he is a boy. Then the child with black hair cannot be a boy and is also lying.
The child with the black hair is the girl and the child with the brown hair is the boy.