# Lesson 2 Relate Addition and Subtraction within 10

Let’s think about the relationship between addition and subtraction.

## Warm-up What Do You Know About …?

What do you know about 10?

## Activity 1 Revisit What’s Behind My Back, 10 Cubes

We are going to play a game you may have played in first grade called What’s Behind My Back?

## Activity 2 Sums of 10

## Problem 1

For each cube tower, write as many equations as you can think of that represent the cubes.

## Problem 2

Find the number that makes each equation true. Then write the letter of the cube tower that represents the equation.

Letter:

Letter:

Letter:

Letter:

Letter:

Letter:

Letter:

Letter:

Letter:

Letter:

## Practice Problem

## Problem 1

Jada is playing “What’s Behind my Back?” with Han. Han has 10 cubes and shows Jada these connecting cubes.

How many connecting cubes are behind Han’s back?

What’s an addition equation that you can write that matches the game?

What’s a subtraction equation that you can write that matches the game?