Lesson objective: Understand that addition and subtraction are related operations.

Students bring prior knowledge of addition and subtraction from 1.OA.C.6. This prior knowledge is extended to include the relationship between the two operations as students solve one problem using both operations. A conceptual challenge students may encounter is undestanding that problems can be solved using the inverse operation.

The concept is developed through work with number lines, which allows students to visualize how the numbers and operations are related.

This work helps students deepen their understanding of operations because they are making connections between the two operations.

Students engage in Mathematical Practice 2 (reason abstractly and quantitatively) as they work to solve one situation using both addition and subtraction.

**Key vocabulary:**

- related
- relationship
- strategy

**Special materials needed:**

- counters (optional)
- cubes (optional)
- student number lines (optional)