Lesson objective: Apply strategies to find the sum of addition problems with three and four two-digit addends.

This lesson provides an opportunity for students to apply their knowledge and understanding of known addition strategies to a mathematical situation. Students are asked to solve addition problems with three and four two-digit addends using previously learned addition strategies. They are required to demonstrate their understanding of these strategies by solving each equation two different ways.

Key Concept students will use:

- A group of addends always has the same sum no matter what strategy we use to add them.

Skills students will use:

- adding multiples of ten (Grade 1, Unit 11)
- an understanding of place value to add (Grade 1, Unit 14)
- applying properties of operations to solve problems (Grade 1, Unit 15)

Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they solve problems using a variety of strategies to contruct different ways to solve the same problem. Mathematical Practice 8 (Look for and express regularity in repeated reasoning) is also featured in this lesson as students use strategies they have practiced in addition problems with two addends and apply them to situations that involve three and four addends.

**Key vocabulary: **

- addend
- compose
- decompose
- strategy