Lesson objective: Fluently add and subtract to 1000 using place value strategies.

This lesson helps to build fluency with whole number addition and subtraction. An open number line is used here because it supports using the inverse operations to solve problems. This work develops students' understanding that you can use the relationship between addition and subtraction to add and subtract within 1000.

Students engage in Mathematical Practice 2 (Reason abstractly and quantitatively) as they create logical representations of the problem at hand and use what they know about the relationship between addition and subtraction to choose which operation would be the most efficient.

**Key vocabulary:**

- addition
- inverse operations
- open number line
- subtraction