This lesson is one of the activities that has been used in Julia Robinson Mathematics Festivals. At most of these festivals there are many pages listing interesting problems, and students come in and choose to work on the problems. The hard part for the teacher is to say more by saying less. It is best to ask a few questions and just encourage the students to think and explore. The list of questions does most of the work.
The problem list and associated lesson plan pdfs may be found at
Building Blocks. We encourage people to add more discussion there.
All of the Julia Robinson Activities are posted at
This lesson was written by Joshua Zucker and Brian Byrne.