Lesson objective: Find volume of irregular solid figures by decomposing into right rectangular prism. Apply generalized volume formulas and add to find volume of irregular figure.

This lesson helps to build procedural skill with adding volume. Irregular figures are used here because they support students' understanding of decomposing into right rectangular prisms to find volume and then add together. This work develops students' understanding that volume is additive.

Students engage in Mathematical Practice 7 (Look for and make use of structure) as they connect the structure to multiplicative reasoning, and the decomposed figures as additive.

**Key vocabulary:**

- additive
- decompose
- volume

**Special materials needed:**

- isometric dot paper
- unit cubes