Prison Challenge

Logic Level 2

A prison warden challenges a death row inmate that he can earn his freedom if he can create a riddle that the warden cannot solve. On the day of his execution, a man comes to visit the prisioner. The prisoner asks for the warden. When the warden comes in the prisoner gives him this riddle about his visitor.

The prisoner says: Brothers and Sisters have I none, But that man's father is my father's son. Who is that man?

Excel in math and science

Master concepts by solving fun, challenging problems.

It's hard to learn from lectures and videos

Learn more effectively through short, conceptual quizzes.

Our wiki is made for math and science

Master advanced concepts through explanations, examples, and problems from the community.

Used and loved by 4 million people

Learn from a vibrant community of students and enthusiasts, including olympiad champions, researchers, and professionals.