Lesson objective: Compute the radius or diameter of a circle given the circumference.

This lesson helps to build procedural skill with the formula for the circumference of a circle. Real life examples, such as bicycle tires and tennis balls, are used here because they support students working with the conceptual understanding of circles. This work develops students' understanding that the relationship between the circumference and diameter of a circle is a constant which we call Pi (π).

Students engage in Mathematical Practice #8 (Look for and express regularity in repeated reasoning) as they solve equations to find the diameter and radius of a circle when given the circumference.

**Key vocabulary:**

- circle
- circumference
- diameter
- radius

**Special materials needed:**

none