Lesson objective: Add numbers within 1000 by decomposing and using a number line.

This lesson helps to build procedural skills with whole number addition. A number line is used here because it supports tracking of multiple addends and looking for efficient jumps to find a sum. This work develops students' understanding that decomposing numbers and choosing to add the decomposed parts in strategic ways can make finding sums more efficient.

Students engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as they look for general methods and efficient strategies or shortcuts by decomposing numbers strategically to make counting up to solve subtraction problems easier based on the starting value.

**Key vocabulary:**

- decomposing
- efficient
- sums