## Lesson: Circumference and Area

Introducing the Concept

Your students know how to find the area of common figures like rectangles, parallelograms, and triangles. Now they will extend their knowledge to finding the area of a circle. Spend some time helping them understand the number pi as the ratio of the circumference of a circle to its diameter. This will help them feel more comfortable with the formula for the circumference of a circle. It will also help them relate pi to the area of a circle.

**Materials:** 5 circular objects of different sizes, such as jar lids, for every two students; string, rulers, and blank paper for all students

**Preparation:** Distribute a set of jar lids to student pairs. Also distribute string, rulers, and blank paper to each student. Have students create a table on their paper similar to the one described and illustrated below.

**Prerequisite Skills:** Students should be able to use a ruler to measure distances.

Draw a picture of a circle on the board or overhead projector and review the definitions for *circle,* *diameter,* and *radius.* Introduce the concept of circumference as perimeter.