Assume they already know it, and ask them to explain it. A good explanation is almost as rare as understanding it. If they don't know it, then ask to solve. T

Assume they already know it, and ask them to explain it. A good explanation is almost as rare as understanding it. If they don't know it, then ask to solve. The early controversy with the Monty Hall problem was that explanations left loopholes, or weren't compelling enough, and even people who who should have known better didn't understand the solution clearly enough.