Lesson objective: Add two-digit and one-digit numbers together using the strategy of composing a new ten when necessary.

This lesson provides an opportunity for students to apply their knowledge and understanding of place value to add numbers in a real-life situation. Students are asked to find the total number of books being packed into each box as the teacher organizes her classroom library.

Key Concept students will use:

- When adding two-digit numbers, we add tens with tens and ones with ones (sometimes composing a ten).

Skills students will use:

- place value knowledge to identify tens and ones (Grade 1, Unit 8)
- strategies for adding two-digit numbers (Grade 1, Unit 11)
- decomposing to add more efficiently (Grade 1, Unit 11)

Students engage in Mathematical Practice 6 (Attend to Precision) as they decompose and combine numbers to make a new ten. Students may use base ten blocks, ten frames or a series of equations to show their steps for adding. Students will strategically decide how to decompose a single-digit number to combine the addends in steps that use multiples of ten.

**Key vocabulary: **

- compose
- decompose
- ones
- sum
- tens

**Special materials needed:**

- base ten blocks (optional)
- ten frames (optional)