# Lesson 14 Think Before You Subtract

Let’s think about decomposing before we subtract.

## Warm-up Which One Doesn’t Belong: Blocks and Blocks and Blocks

Which one doesn’t belong?

## Activity 1 Agree to Disagree

Tyler and Clare are subtracting by place to find the value of

The diagrams show each student’s first step.

Tyler:

Clare:

What is the same about Tyler and Clare’s diagrams? What is different?

Work together to complete Tyler’s way and Clare’s way to find the value of

. What do Tyler and Clare’s diagrams look like after the last step? What is the same about these diagrams? What is different?

## Activity 2 Sort and Subtract

Here is a base-ten diagram for 341.

Andre wants to use diagrams and subtract by place to find the value of

. He says he will decompose a ten and a hundred to subtract. Why do you think he said that? Andre only wants to use a diagram to subtract by place if he will decompose a unit. Help Andre sort the expressions into groups. If you are not sure, use base-ten blocks or a diagram to help.

decompose 2 units

decompose 1 unit

do not decompose

Find the value of 1 expression from each group. Show your thinking.

## Practice Problem

## Problem 1

Jada is finding the value of