Lesson 3 Relate Addition and Subtraction within 20
Let’s find the number that makes equations with 20 true.
Warm-up Number Talk: Addition and Subtraction
Find the value of each expression mentally.
Activity 1 Introduce What’s Behind My Back: 20 Cubes
We are going to play What’s Behind My Back, this time with 20 cubes.
Activity 2 Make the Equation True
Find the number that makes each equation true.
If you have time:
Practice Problem
Problem 1
Find the number that makes each equation true. Show your thinking using drawings, numbers, or words.