Lesson objective: Compute perimeters of scale drawings using scale factors.

This lesson helps to build procedural skill with determining scale values. A rectangle is used here because it enables students to see how the changing dimensions change the perimeter by the same proportion. This work develops students' understanding that lengths of sides of pairs of scale drawings are proportional, resulting in proportional perimeters.

Students engage in Mathematical Practice 4 (model with mathematics) as they manipulate the lengths of rectangles to determine the change in perimeter and the relationship between the perimeters and the dimensions.

**Key vocabulary:**

- original figure
- perimeter
- proportion
- scale drawing
- scale factor