Lesson objective: Add the area of two smaller rectangles to compute the area of a larger rectangle.

This lesson helps to build procedural skill with using the distributive property to solve area problems. The area model is used here because it supports decomposing the length of a rectangle. 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 use the area model to practice decomposing the length or width of a rectangle to find the area of two smaller rectangles in order to find the total area of the whole rectangle.

**Key vocabulary:**

- area
- area model
- length
- multiplication
- width

**Special Materials Needed:**

- one-inch grid paper
- one-inch tiles