Lesson objective: Add and subtract three-digit numbers without regrouping.

This lesson helps to build fluency with whole number three-digit addition and subtraction without regrouping. Base ten blocks and number lines are used here because they support strategies related to place value and decomposition of numbers. This work develops students' understanding that strategies related to two-digit addition and subtract can be applied to three-digit addition and subtraction.

Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they apply different strategies to solve three-digit addition and subtraction problems, including the use of multiple tools such as base ten blocks and number lines.

**Key vocabulary:**

- base ten blocks
- decompose
- digit
- hundreds
- number line
- ones
- place value
- tens