Lesson 5
Compose and Decompose Numbers Within 1,000
Warmup: What Do You Know About 308? (10 minutes)
Narrative
The purpose of this What Do You Know About _____ is to invite students to share what they know about and how they can represent the number 308. Students use place value understanding as they describe the meaning of the digits in 308 and the different ways they can represent the number (MP7).
Launch
 Display the number.
Activity
 “What do you know about 308?”
 1 minute: quiet think time
 Record responses.
Student Facing
Student Response
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Activity Synthesis
 “What are different ways we could represent 308?”
 If it doesn’t come up in student responses, consider asking:
 “What do you think someone means if they said 308 has no tens? Would you agree?”
 “Is there a way we could represent 308 with tens? ”
Activity 1: How Many Did You Get? (15 minutes)
Narrative
The purpose of this activity is for students to represent numbers in different ways. The structure of the task encourages students to practice composing units and decomposing units. Students also have opportunities to use and connect concrete and abstract representations of threedigit numbers (MP2).
Supports accessibility for: Memory, Organization
Required Materials
Materials to Gather
Launch
 Groups of 2
 Give baseten blocks to each group.
Activity
 “We are going to represent numbers in different ways. Start with baseten blocks, but you may use diagrams, symbols, or other representations to show your number.”
 8 minutes: partner work time
 Consider taking a picture of groups’ blocks before and after they compose or decompose units for use in the synthesis.
Student Facing

Start with 2 hundreds. Grab a handful of tens and of ones.
 What number do your baseten blocks represent? _______

Represent the same number in another way. Show your thinking using diagrams, symbols, or other representations.

Combine your blocks with your partner’s blocks.
 What number do your baseten blocks represent? _______

Represent the same number in another way. Show your thinking using diagrams, symbols, or other representations.

Represent your group’s number in the following ways:

without hundreds

without tens

without hundreds or tens

Student Response
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Activity Synthesis
 Display a picture or drawing of a group’s blocks before they composed or decomposed units, such as:
 “How could this group represent their number in another way?” (exchange 1 of the tens for 10 ones, exchange 10 tens for 1 hundred)
 Display a picture or drawing of a group’s blocks that uses the fewest number of blocks, such as:
 “How could this group represent their number in another way?” (exchange 1 of the hundreds for 10 tens, exchange 1 ten for 10 ones, exchange all the tens for 40 ones)
Activity 2: Let Me Count the Ways (20 minutes)
Narrative
The purpose of this activity is for students to represent the same number in multiple ways. During the gallery walk, students are encouraged to connect different representations of a number that make use of structure in similar ways (for example, connecting a diagram and an equation that show the number using the same number of hundreds, tens, and ones). The lesson synthesis focuses on the different ways students represent 356 with expressions or equations. Students demonstrate their understanding of the structure of the baseten system when they describe, compare, and connect different representations of the same threedigit number (MP7).
This activity uses MLR7 Compare and Connect. Advances: representing, conversing
Required Materials
Materials to Gather
Launch
 Groups of 3–4
 Give each group a piece of chart paper and markers.
Activity
 “Represent 356 in at least 3 different ways. You may use diagrams, symbols, or other representations. If you have time, you can represent 356 in more than 3 ways.”
 5 minutes: independent work time
 “Share your representations with your group. Work together to put each different way on your group’s poster. If you have time, you may add other ways to represent the number.”
 5 minutes: group work time
 “You are going to rotate to see other group’s posters. One person from your group should place a checkmark next to any representation your team also used to show 356.”
 Prompt groups to rotate to the next chart every 1 minute.
Student Facing
 Represent 356 in at least 3 different ways. Show your thinking using diagrams, symbols, or other representations.
 Create a poster with your group to show 356 in different ways.
Student Response
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Advancing Student Thinking
 “How could you represent this number with equations?”
 “How could you represent this number with words?”
 “How could you represent this number with digits?”
Activity Synthesis
 Display:
 3 hundreds + 4 tens + 16 ones
 “Does this expression show 356? Explain.” (Yes. 16 ones is the same as one ten and 6 ones so it’s the same as 3 hundreds 5 tens and 6 ones.)
 “This is one way we could show 356 as an expression. What other ways did you see groups represent 356 as an expression?”
 Record responses.
 “How are the expressions the same? How are they different?” (They all show 356. Some expressions have different amounts of hundreds and tens. Some expressions use words.)
 30 seconds: quiet think time
 2 minute: partner discussion
 Share responses.
Lesson Synthesis
Lesson Synthesis
“Today we represented numbers with baseten blocks, drawings, words, and equations. We composed larger units from smaller units and we decomposed larger units into smaller units.”
“Why do you think it is important to be able to represent numbers in different ways?” (It can help you understand place value and numbers better. You may need to do it if you add or subtract numbers.)
Cooldown: Two Hundred SixtyThree (5 minutes)
CoolDown
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