Lesson objective: Understand that addition and subtraction strategies used with two-digit numbers can be applied to three-digit numbers.

Students bring prior knowledge of adding and subtracting using place value from 2.NBT.B.5. This prior knowledge is extended to adding and subtracting three-digit numbers as students apply two-digit addition and subtraction strategies to three-digit numbers. A conceptual challenge students may encounter is adding and subtracting hundreds.

The concept is developed through work with base ten blocks and number lines, which supports the idea that numbers can be added and subtracted based on place value and decomposition strategies.

This work helps students deepen their understanding of operations because students are provided with multiple ways to represent and model problem situations.

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