In this lesson, students practice composing and decomposing irregular regions to calculate their area, in preparation for estimating the area of circles in the next lesson. In the first activity, the region is polygonal, and students can calculate an exact answer for the area of the floorplan. In the second activity, students must approximate the area of the region.

Students use polygons to model regions on a map or floorplan (MP4). To complete each task, students need to identify relevant information, choose an appropriate strategy, and make simplifying assumptions. Students also have an opportunity to think about what factors affect the estimates. Students see that the accuracy of an estimate is affected by:

• The nature of the information they have or could obtain.
• The assumptions they make.
• The estimation methods they use.