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