# Lesson 2

Relate Addition and Subtraction within 10

### Lesson Purpose

The purpose of this lesson is for students to find the number that makes equations true and write addition and related subtraction equations within 10.

### Lesson Narrative

In previous grades, students learned to find the number that makes 10 when added to a given number and to make a ten to add within 20 and 100. The ability to look for and use sums that have a value of 10 is a foundational skill for the grade 2 benchmark of fluency within 20 and for adding and subtracting within 1,000 using methods based on place value.

In this lesson, students revisit a center activity, What's Behind My Back, and use connecting cubes to elicit their understanding of sums that a value of 10 and the relationship between addition and subtraction. Students will continue practice recognizing and using these sums in lesson activities throughout the unit.

Math Community

Tell students they will have an opportunity to revise their math community ideas at the end of this lesson, so as they work today they should think about actions that may be missing from the current list.

• Action and Expression
• MLR8

Activity 2: Sums of 10

### Learning Goals

Teacher Facing

• Find the number that makes equations within 20 true.
• Write equations with unknown addends and sums of 10 and their related subtraction equations.

### Required Materials

Materials to Gather

Materials to Copy

• What's Behind My Back Stage 2 Recording Sheet Grade 1

### Required Preparation

Activity 1:

• Gather a tower of 10 connecting cubes to use in the launch.

Building On

Building Towards

### Lesson Timeline

 Warm-up 10 min Activity 1 20 min Activity 2 15 min Lesson Synthesis 10 min Cool-down 5 min

### Teacher Reflection Questions

How are you facilitating the creation of a productive mathematical community? Where can you point to evidence of this for students to see?

### Suggested Centers

• Number Puzzles: Addition and Subtraction (1–4), Stage 1: Within 10 (Supporting)