Almost everyone I know could not solve it correctly without a lot of hints. Even when you say: „It is not the answer you first think it is“. I like to use it when someone feels too smart and won’t acknowledge that he might be wrong about something. For example, a friend was arguing that the moon landing didn’t happen because the capsule was too small to hold the needed fuel. I asked him the paradox, he got it wrong. I followed with: „how can you believe to be right about rocket science, when you weren’t able to get this simple question right?“