Lesson objective: Understanding that place value can help us add and subtract numbers more fluently.

Students bring prior knowledge of place value from 2.NBT.1. This prior knowledge is extended to include how thinking about the number of tens and one in a number can help us add and subtract faster. A conceptual challenge students may encounter is believing a number can only be decomposed one way.

The concept is developed through work with a number line, which shows that numbers can be decomposed in different ways.

This work helps students deepen their understanding of numbers because students will gain a deeper understanding of how and why we decompose numbers while adding and subtracting.

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

**Key vocabulary:**

- addition
- subtraction
- addend
- total
- subtrahend
- minuend
- difference