You don’t need a polygraph to solve this problem. The moment you look at this problem, you immediately tend focus on the final part of the question “who is the boy and who is the girl?” Instead, you need to look at the big picture. Try Reading the question again,
“A boy and a girl are talking. One of them lied about their gender. Who is the boy and who is the girl?”
There are 3 points to note:
- There is one boy and one girl.
- One of them lied.
- The lie is about the person’s gender.
While all these statements are true, they complement each other. What if one of these statements is only half true? What if the first statement is half true? That would simply collapse the whole point of this puzzle and so is the third statement. If the second statement is half true, find the other half of the truth. Assuming that the other half of the statement is withheld, you can go following conclusion.
If you were to consider the idea that only one of them has lied, then they’d both be boys or both be girls. Preserving the purpose of the problem, you can imply that –
They both lied(Answer).