Lesson objective: Solve problems that require you to find the one number that you add to another number to make 10.

This lesson provides an opportunity for students to apply their knowledge and understanding of composing 10 to a real-life situation. Students are asked to find the number of fish that are hidden behind a rock in a tank with some fish showing and 10 fish in all.

Key Concept students will use:

- For any number one to nine, there is one number we can add to it to get 10.

Skills students will use:

- Counting objects (Kindergarten, Unit 2)
- Understanding addition as adding to (Kindergarten, Unit 4)
- Decomposing objects within five (Kindergarten, Unit 6)

Students engage in Mathematical Practice 7 (Look for and make use of structure) as they notice that there is only one number that is added to each number one to nine that will make 10. The ability to make 10 is also foundational to place value understanding.

**Key vocabulary: **

- compose
- count on
- decompose
- make a 10