Lesson objective: Understand that we can use both addition and subtraction to solve many kinds of problems.

Students bring prior knowledge of using objects and drawing to solve a variety of situational problems involving addition and subtraction from Grade 1, Unit 9, 1.OA.A.1. This prior knowledge is extended to include classifying some situations as both addition and subtraction as students use either operation to solve. A conceptual challenge students may encounter is interpreting word problems and creating equations to solve.

The concept is developed through work with number bonds and tape diagrams to help students interpret and classify the word problems.

This work helps students deepen their understanding of operations because students learn to interpret word problems based on thinking and making sense rather than key words. As they make meaning of the situations they create connect it to the operations and create appropriate operations.

Students engage in Mathematical Practice #3 (construct viable arguments and understand the reasoning of others) as they defend the equations they created and discuss the relationship between addition and subtraction.

**Key vocabulary:**

- Addend (Unknown addend)
- Terms for main types of addition and subtraction situations: Add to, Take from, Put Together/Take Apart (*Students do not have to know these terms, but an understanding the variety of problem types may help in facilitating class conversations.)

**Special materials needed:**

- concrete manipulatives (for representing the action in story problems, as needed)