Lesson objective: Fluently apply the associative and commutative properties to algebraic expressions.

This lesson helps to build fluency with using the associative and commutative properties to simplify algebraic expressions. Variables are represented as groups of objects (bags of marbles) because it helps students understand the meaning of "like terms" using the context of groups of real-world objects. This work develops students' understanding that the associative and commutative properties apply to algebraic expressions just as they do to numeric expressions.

Students engage in Mathematical Practice 7 (look for and make use of structure) as they use the associative and commutative properties to rewrite algebraic expressions so they are in simplest form. Students see that the simplified expression and the original expression look different but both represent the same value.

**Key vocabulary:**

- associative
- commutative
- expression
- like terms
- variable