This is an activity that can be used as a warm-up, review, or practice after learning about rational and irrational numbers. There are seven problems and answers plus one problem that is open-ended for students to create. Each of the seven problems students decide which number does not belong and discuss WHY it does not belong, reinforcing the definition of rational or irrational numbers. This can be used as a class, pairs, group activity, math station or any way that suits your class best. Answers are provided.