Unit 7, Lesson 9
Add 3-Digit Numbers
Grade 2
Warm-up
10 mins
Number Talk: Ten and Some More
Standards Alignment
Building On
Addressing
2.NBT.7
Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method. Understand that in adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds.
Building Toward
Instructional Routines
Number TalkMaterials
NoneActivity Narrative
The purpose of this Number Talk is to elicit strategies and understandings students have for making a ten when adding a one-digit number to a three-digit number. In the Activity Synthesis, the focus is on how students look for ways to make a ten. These understandings help students develop fluency and will be helpful in the lesson as students add 2 three-digit numbers and consider composing units.
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 Task Statement
Find the value of each expression mentally.
Activity Synthesis
- “What do you notice about the sums?” (I made a ten to find the sum. They all show adding some ones to three-digit numbers. There’s a pattern in the ones—0 ones, 5 ones, 0 ones, 5 ones.)
- “Why are
Activity 1
20 mins
How Did You Add 3-Digit Numbers?
Instructional Routines
MLR8 Discussion SupportsMaterials
To Gather
Base-ten blocksActivity Narrative
The purpose of this activity is for students to practice adding within 1,000, with an emphasis on adding by place. Throughout the activity, students have opportunities to explain their methods and representations to peers. In the Activity Synthesis, students have opportunities to question and critique the work of their peers as they compare different methods for adding three-digit numbers and different representations that show composing units when adding by place (MP3).
This activity uses MLR8 Discussion Supports. Advances: conversing.
Engagement: Provide Access by Recruiting Interest.Provide choice. Invite students to decide with which problem to start and the strategy with which they feel most comfortable solving.
Supports accessibility for: Social-Emotional Functioning, Organization, Attention
Supports accessibility for: Social-Emotional Functioning, Organization, Attention
Activity 2
15 mins
Analyze and Add
Instructional Routines
NoneMaterials
To Gather
Base-ten blocksActivity Narrative
The purpose of this activity is for students to analyze two methods for finding a sum within 1,000. Students use what they know about adding by place and composing units to determine which method shows the correct value of the sum. Students discuss why one method did not work and how the method could be adjusted to find the correct sum (MP3).
Launch
- Groups of 2
- Give students access to base-ten blocks.
Activity
- “Noah and Kiran were asked to find the value of
- 1–2 minutes: quiet think time
- “Discuss how Noah’s and Kiran’s work is the same and how their work is different. Then explain which student found the correct value of the sum. Show how you know.”
- 10 minutes: partner work time
- Monitor for groups that match Kiran’s equations to Noah’s diagram to explain how Noah could improve his work.
Lesson Synthesis
Display Kiran’s way and any work samples that show methods different from those in Activity 1.
“Today we added 2 three-digit numbers and looked at different methods and representations.”
“How are the methods and representations you saw today the same? How are they different?”
“Which method do you prefer? Which would you like to practice more?”
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