Lesson objective: Fluently solve addition and subtraction problems using an understanding of place value.

This lesson helps to build fluency with number decomposition. Decomposing numbers is used here because makes the numbers in the problem easier to work with. This work develops students' understanding that if you decompose a number before adding or subtracting it will make the problem easier to solve.

Students engage in Mathematical Practice 1 (Understand problems and perservere in solving them) as they decompose numbers before adding or subtracting them.

**Key vocabulary:**

- decompose
- addend
- total
- difference