Lesson 7
Subtract Your Way
Warmup: Number Talk: Subtract TwoDigit Numbers (10 minutes)
Narrative
The purpose of this Number Talk is to elicit strategies and understandings students have for subtracting numbers within 1,000. These understandings help students develop fluency and will be helpful as students relate subtraction algorithms to strategies they have used to subtract within 1,000.
Launch
 Display one expression.
 “Give me a signal when you have an answer and can explain how you got it.”
 1 minute: quiet think time
Activity
 Record answers and strategy.
 Keep expressions and work displayed.
 Repeat with each expression.
Student Facing
Find the value of each expression mentally.
 \(50  10\)
 \(58  10\)
 \(258  20\)
 \(258  24\)
Student Response
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Activity Synthesis
 “How was place value helpful as you subtracted these numbers?” (When we were subtracting 10, only the tens place changed. For the last expression we were able to subtract the tens, then the ones.)
 Consider asking:
 “Who can restate _____'s reasoning in a different way?”
 “Did anyone have the same strategy but would explain it differently?”
 “Did anyone approach the problem in a different way?”
 “Does anyone want to add on to _____’s strategy?”
Activity 1: Strategies to Subtract (25 minutes)
Narrative
The purpose of this activity is for students to subtract numbers within 1,000 using any strategy that makes sense to them to find the difference of two numbers within 1,000. The expressions in this activity give students a chance to use different strategies, such as subtracting hundreds from hundreds, tens from tens, and ones from ones, or adding up. Students may also use a variety of representations, which will be the focus of the activity synthesis. Students who choose to use baseten blocks or number lines to represent their thinking use tools strategically (MP5).
This activity uses MLR7 Compare and Connect.
Advances: Representing, Conversing
Supports accessibility for: SocialEmotional Functioning and Fine Motor Skills
Required Materials
Materials to Gather
Launch
 Groups of 2
 Give students access to baseten blocks.
 “Take a minute to think about how you could subtract these numbers.”
 1 minute: quiet think time
 Share responses.
Activity
 “Work with your partner to subtract these numbers in any way that makes sense to you. Explain or show your reasoning.”
 5–7 minutes: partner work time
 Monitor for an expression for which students use a variety of representations, such as:
 using baseten blocks
 drawing a number line
 writing their reasoning in words
 writing equations
 During the synthesis, students will create a visual display that shows how they found the value of the selected expression.
 Give each group tools for creating a visual display.
Student Facing
Find the value of each difference in any way that makes sense to you. Explain or show your reasoning.
 \(428  213\)
 \(505  398\)
 \(394  127\)
Student Response
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Activity Synthesis
MLR7 Compare and Connect
 “Create a visual display that shows how you found the value of ______. You may want to include details such as notes, diagrams, drawings, and so on, to help others understand your thinking.”
 2–5 minutes: partner work time
 5–7 minutes: gallery walk
 “What is the same and what is different about the ways that groups represented the subtraction?” (Some groups used equations. Some groups used baseten blocks. They all used the same numbers. They all got the same answer.)
 Display one example of 2–3 different representations sidebyside for all to see.

“Which representations show the same idea or help us find the difference the same way?” (The number line and equations show the same idea of adding up. The baseten blocks are different because they show a ten or a hundred decomposed into smaller units before some of the blocks are taken away.)
Activity 2: Baseten Drawings (10 minutes)
Narrative
The purpose of this activity is for students to make sense of drawings of baseten blocks. Students compare two baseten drawings. The first drawing is the same as what they saw in grade 2, where the tens block is decomposed into 10 individual ones and moved over to the ones place before subtracting the ones. In the second drawing, the tens block is moved over and partitioned into 10 parts but not decomposed into individual ones. The subtraction of ones is shown directly on the ten that was moved over. Students then match baseten diagrams to subtraction expressions and subtract to find the value of each expression. This will be helpful in later lessons when students relate baseten diagrams to written algorithms.
Advances: Speaking
Launch
 Groups of 2
 “Take a minute to look at the drawings of how Jada and Han used baseten blocks to subtract.”
 1 minute: quiet think time
 “Discuss with your partner how Jada and Han’s drawings are alike and how they are different.”
 1 minute: partner discussion
 Share responses.
Activity
 “Work together to match each expression with a diagram that represents it. Then, find the value of each expression.”
 3–5 minutes: partner work time
Student Facing

Jada and Han made drawings to show how they used baseten blocks to find the value of \(262  135\). Their drawings are shown.
Jada's drawing
Han's drawing
How are their drawings alike? How are they different?

Here are three expressions, followed by three diagrams. Write each expression next to the diagram that represents it. Then, find the value of the expression.
\(252  181\)
\(262  135\)
\(252  132\)
Student Response
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Activity Synthesis
 Invite students to share the expression that matches each diagram.
 “What did you have to pay attention to as you matched each diagram to an expression?” (I had to look for the numbers that were being subtracted. I had to look for tens over by the ones and hundreds over by the tens if there weren’t enough tens or ones.)
Lesson Synthesis
Lesson Synthesis
“Today we subtracted numbers using many different strategies. What is your favorite representation to use to subtract numbers?” (I like to use baseten blocks so I can see the numbers I am subtracting. I like to write equations because it shows me how I am subtracting the numbers.)
“Does the way you subtract numbers or the representation you use change based on the numbers in the problem?” (Yes, I use mental math when I see that one of the numbers is close to a hundred. No, I always add up. I always like to use baseten blocks.)
“Keep all these strategies in mind as we learn new ways to show our reasoning around subtraction in the upcoming lessons.”
Cooldown: Subtract within 1,000 (5 minutes)
CoolDown
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