Lesson objective: Find the area of a rectangle by decomposing one of the side lengths.

This lesson helps to build procedural skill with the distributive property. The area model is used here because it supports decomposing rectangles. This work develops students' understanding that the area of a rectangle with whole-number side lengths a and b + c is the sum of a x b and a x c.

Students engage in Mathematical Practice 7 (Look for and make use of structure) as they they use the area model to decompose rectangles, find the area of the two smaller rectangle within, and add the area of each to find the area of the whole rectangle.

**Key vocabulary:**

- area
- columns
- multiplication
- rows

**Special materials needed:**