Lesson objective: Solve addition and subtraction problems mentally.

This lesson provides an opportunity for students to apply their knowledge and understanding of addition and subtraction strategies to a real-world situation. Students are asked to mentally calculate if Sam can afford all three snacks and how much change she should receive.

Key Concept students will use:

- The strategy we use to add or subtract does not change the total or difference.

Skills students will use:

- Using Addition and Subtraction Strategies (Grade 1, Unit 6)
- Adding and Subtracting Within 100 (Grade 2, Unit 1)

Students engage in Mathematical Practice 6 (Attend to precision) as they solve addition and subtraction problems mentally.

**Key vocabulary: **

- mentally
- difference
- total