Lesson 3
Compose Threedigit Numbers
Warmup: Number Talk: Add Tens and Ones (10 minutes)
Narrative
The purpose of this Number Talk is to elicit strategies and understandings students have for adding by place and composing a ten mentally. These understandings help students develop fluency and will be helpful later in this lesson when students describe baseten representations by place and use the fewest number of baseten blocks to represent a number.
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 strategies.
 Keep expressions and work displayed.
 Repeat with each expression.
Student Facing
Find the value of each expression mentally.
 \(42+42\)
 \(21+63\)
 \(50+34\)
 \(48+36\)
Student Response
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Activity Synthesis
 “What did you notice about the sums?” (The expressions were all different, but all had a value of 84.)
 “How could you explain why the third and fourth expressions have the same value?” (You could take 2 ones from 36 and add it to 48 to make \(50+34\).)
Activity 1: Sort Blocks by Value (20 minutes)
Narrative
In this activity, students sort baseten blocks and record the total number of blocks they have by the unit each block represents. Students work together to look for ways to compose larger units from smaller units in order to represent the same value with the fewest number of blocks (MP7). They represent composing a hundred by exchanging 10 ten blocks for a hundred block and represent composing a ten by exchanging 10 one blocks for a ten block. In the synthesis, students compare different ways that groups represent the total value which may include representing the value as a threedigit number.
This activity uses MLR7 Compare and Connect. Advances: representing, conversing
Required Materials
Materials to Gather
Required Preparation
 Each group of 3–4 students will need a container with 2 hundreds, 28 tens, and 15 ones.
 Each group of 3–4 students will need access to additional baseten blocks (hundred blocks and ten blocks).
Launch
 Groups of 3–4
 Give each group a container of blocks, access to baseten blocks, and supplies for making a group display.
Activity
 “Your group has a container of baseten blocks.”
 “Sort the blocks by the unit they represent and record the number of each type of block on your paper.”
 “Work together to figure out how to represent the same total value using the fewest number of blocks possible.”
 6 minutes: smallgroup work time
MLR7 Compare and Connect
 “Create a visual display to show the total value of the blocks. Include details such as diagrams, labels, and numbers to help others understand your thinking.”
 2–5 minutes: group work time
 “As you look at other groups’ representations, look for different ways groups show the value. Which ways are the same as your group’s representation? Which ways are different? How do you know they represent the same value?”
 5 minutes: gallery walk
 “Discuss any revisions you would like to make to your representations with your group.”
 1–2 minutes: smallgroup work time
 Monitor for students who:
 create a baseten diagram with the fewest amount of blocks represented
 write 4 hundreds, 9 tens, 5 ones
 write 495
 use an expression such as \(400 + 95\) or \(400 + 90 + 5\)
Student Facing

Sort the blocks.

We have _________ hundreds.

We have _________ tens.

We have _________ ones.


Represent the same value with the fewest number of blocks possible.

We have _________ hundreds.

We have _________ tens.

We have _________ ones.

 Represent the value of your blocks using baseten diagrams, words, or numbers.
Student Response
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Advancing Student Thinking
If students represent their number with 10 or more of any unit, consider asking:
 “How do you know that you have used the fewest number of blocks possible?”
 “How can you combine the tens or ones so you don’t use as many of the baseten blocks?”
Activity Synthesis
 Display previously identified students’ representations.
 “What is the same and what is different between the ways groups represented the total value of the blocks?” (They each show 4 hundreds, 9 tens, and 5 ones. Some just use diagrams, some use only digits, some use diagrams, numbers, and expressions.)
Activity 2: The Same But Different (15 minutes)
Narrative
In this activity, students build on their work with baseten blocks in previous activities to use baseten diagrams to represent a value using the fewest number of each unit possible. They first interpret images of students’ representations of a number using baseten blocks. When representing the same value, students may choose to draw the original representation and show composing units by circling groups of 10 tens or 10 ones. Others may choose other methods, such as circling or labeling the images to show ways to compose a larger unit or by using what they have learned about patterns in units from previous lessons. In the synthesis, students connect the 3 digits in a threedigit numeral to their representations (MP7).
Supports accessibility for: Organization
Required Materials
Materials to Gather
Launch
 Groups of 2
 Give students access to baseten blocks.
Activity
 “Mai and Diego each used baseten blocks to represent numbers.”
 “Record the number of hundreds, tens, and ones each student used.”
 “Find a way to represent the same value with the fewest number of each unit possible and represent it using a baseten diagram.”
 “Use blocks if it helps.”
 “Together with your partner, figure out the total value of the blocks.”
 8 minutes: partner work time
 Monitor for students who write the total as a threedigit number.
Student Facing
Mai’s Blocks

Mai has ______ hundreds _____ tens _____ ones.
 Draw a baseten diagram to represent the same total value with the fewest number of each unit.

What is the value of Mai’s blocks?
Diego’s Blocks

Diego has ______ hundreds _____ tens _____ ones.
 Draw a baseten diagram to represent the same total value with the fewest number of each unit.
 What is the value of Diego’s blocks?
Student Response
For access, consult one of our IM Certified Partners.
Activity Synthesis
 “How many did Diego have in all? Explain how you knew.”
 Select previously identified students to share.
 Write 283 while saying “2 hundreds, 8 tens, and 3 ones.”
 “This is a threedigit number. The digits represent amounts of hundreds, tens, and ones.”
 As needed, demonstrate reading the number left to right and gesture to emphasize the value of each digit.
Lesson Synthesis
Lesson Synthesis
“Today you represented numbers that were greater than 100 using baseten blocks, baseten diagrams, numbers, and words.”
“You also saw how you can write a threedigit number to represent the amount of hundreds, tens, and ones.”
Display 324.
“How would you represent this number with baseten blocks or a baseten diagram? Explain how you know.” (I’d draw 3 hundreds, 2 tens, and 4 ones. The first digit shows how many hundreds, the second digit shows how many tens, and the last digit shows how many ones.)
Cooldown: How Many Blocks? (5 minutes)
CoolDown
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