Lesson objective: Compare strategies for adding and subtracting to look for efficient strategies.

This lesson provides an opportunity for students to apply their knowledge and understanding of place value and decomposition to a mathematical situation. Students are asked to compare student strategies to look for efficient strategies of addition and subtraction.

Key Concept students will use:

- Use place value understanding and decomposition to add and subtract using a variety of strategies.

Skills students will use:

- Use concrete models and drawings to understand that it is sometimes necessary to compose and decompose numbers when adding and subtracting. (Grade 2, Unit 11)
- Use counting up (recognizing the inverse relationship of addition and subtraction) to solve subtraction problems.
- Using decomposing to strategically count up or compensate numbers to make adding or subtracting more efficient.

Students engage in Mathematical Practice 7 (Look for and make use of structure) as they decompose numbers using their place values, and they use those values in different ways to most efficiently solve a subtraction problem.

**Key vocabulary: **

- compensation
- decompose
- difference
- efficient

**Special materials needed:**