Lesson 2 Find the Unknown Addend

- Let’s find values that make the equations true.

Warm-up Choral Count: Count Back by 10

Count back by 10, starting at 97.
What patterns do you see?

Activity 1 How Did You Find It?

What is the same and what is different between these tools?
Find the number that makes the equation true. Show your thinking using the cubes, blocks, or drawings.

$41 +$ $= 84$

Activity 2 You Go This Way, I’ll Go That Way

Han and Mai use blocks to find the number that makes the equation true.

$17 +$ $= 48$

Han starts by using blocks to show 17. Show how he could find the number that makes the equation true.
Mai starts by using blocks to show 48. Show how she could find the number that makes the equation true.
Try this one on your own. Choose who will start with 21 and who will start with 96.
$21 +$ $= 96$
Show your partner how you found the number that makes the equation true.

Practice Problem

Problem 1

Find the number that makes each equation true in a way that makes sense to you. Show your thinking.

$26 + 51 =$
$35 +$ $= 67$