Lesson 8
Compose Tens and Hundreds to Add
Warmup: How Many Do You See: Too Many Tens (10 minutes)
Narrative
The purpose of this How Many Do You See is to allow students to use grouping strategies to describe amounts represented with baseten diagrams. Students look for and make use of structure (MP7) when they describe how many they see in terms of place value and how they mentally compose new units to name how many they see.
Launch
 Groups of 2
 “How many do you see? How do you see them?”
 Flash the image.
 30 seconds: quiet think time
Activity
 Display the image.
 “Discuss your thinking with your partner.”
 1 minute: partner discussion
 Record responses.
 Repeat for each image.
Student Facing
How many do you see? How do you see them?
Student Response
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Activity Synthesis
 “How were the images the same? How were they different?” (The first two had the same number of tens. I saw a group of three ones in each image. They each showed different values. The last image had more than 10 tens.)
 “What would you need to do to show the value of the third image with the least amount of blocks?” (If you were using blocks, you could exchange 10 tens for 1 hundred. Use one hundred instead of 10 tens.)
Activity 1: Compare the Sums (20 minutes)
Narrative
The purpose of this activity is for students to find the sum of a twodigit and a threedigit number when both a ten and a hundred are composed when adding by place. They find the value of each sum in a string of expressions, where the first addend remains the same, but the second addend changes. These variations result in composing a ten, composing a hundred, and composing both a ten and a hundred.
Although the number choices encourage students to consider adding by place, they may use any method that makes sense to them when finding the value of each sum. Students share their thinking with a partner and explain why their method works (MP3). The lesson synthesis focuses on students sharing and making sense of strategies based on place value and using place value language to describe what they noticed about the sums and composing larger units (MP7).
This activity uses MLR8 Discussion Supports. Advances: conversing
Supports accessibility for: Language, Organization, SocialEmotional Functioning
Required Materials
Materials to Gather
Launch
 Groups of 2
 Give students access to baseten blocks.
Activity
 “Find the value of each sum. Show your thinking using diagrams, symbols, or other representations. Use baseten blocks if it helps. After you find each sum, compare your method to your partner’s.”
 Display sentence frames to support students when they compare methods:
 “We have the same sum, but ...”
 “We have different sums because …”
 “Our thinking is the same because …”
 “Our thinking is different because …”
 12 minutes: partner work time
 Monitor for students who find the sum of \(273 + 88\) by grouping by place value using baseten blocks or a baseten diagram.
Student Facing
Find the value of each sum. Show your thinking. Use baseten blocks if it helps.
 \(273 + 18\)
 \(273 + 81\)
 \(273 + 88\)
 What was the same and different about the sums?
Student Response
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Activity Synthesis
 Invite previously identified students to share their work for \(273 + 88\).
 “How did _____ find the sum?”
 “What was the same and different about what you did to find the value of each sum?” (We had to make a ten and a hundred for the last one. For the first 2, we just had to make a ten or a hundred.)
Activity 2: Different Ways to Show Your Thinking (15 minutes)
Narrative
Required Materials
Materials to Gather
Launch
 Groups of 2
 Give students access to baseten blocks.
Activity
 “Priya and Lin were asked to find the value of \(358 + 67\). They represented their thinking in different ways. What is the same and different about their representations?” (Priya used the diagrams and wrote equations. Priya circled the new units she made in her diagram. Lin wrote the units and added them first. They found the same value.)
 5 minutes: partner discussion
 “Where do you see each student composing new units?” (Priya circled 10 tens to show a new hundred and circled 10 ones to show a new ten. Lin added the units and has 11 tens and 11 ones. 11 tens is the same as 1 hundred and 1 ten and 11 ones is the same as 1 ten and 1 one.)
 30 seconds: quiet think time
 1 minute: partner discussion
 Share and record responses.
 “Now you are going to find the value of \(546 + 86\) and represent your thinking.”
 5 minutes: independent work time
 Monitor for students who represent place value strategies using:
 baseten blocks or baseten diagrams
 equations in unit form
 equations with only numbers
Student Facing

Priya and Lin were asked to find the value of \(358 + 67\).
Priya's work
Lin's work
What do you notice about their work? What is the same and different about their representations? Be prepared to explain your thinking.
 Find the value of \(546 + 86\).
Show your thinking. Use baseten blocks if it helps.
Student Response
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Advancing Student Thinking
Activity Synthesis
 Invite previously identified students to share their work.
 “What’s the same across these representations? What is different?” (They all got the same answer. They all made a ten and a hundred. Some used words, some used diagrams, and some used only numbers.)
Lesson Synthesis
Lesson Synthesis
“Today you learned that sometimes you need to make a ten and a hundred when adding. We also saw that there are different ways to represent our thinking.”
“Which representations do you find most helpful to show your thinking? Why?”
Cooldown: Make Tens and Hundreds (5 minutes)
CoolDown
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