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Add Within 1,000!

Grade 2: Unit 7: Lesson 10

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Goals:

Add numbers within 1,000 using strategies based on place value and the properties of operations.

Purpose:

The purpose of this lesson is for students to add three-digit numbers using strategies based on place value and the properties of operations.

Narrative:

In previous lessons, students used properties of operations, their understanding of the count sequence, and their understanding of place value to add within 1,000. They used different methods and representations to add by place and compose tens and hundreds. In this lesson, students choose their own methods for adding within 1,000 and share their methods with their peers. They also have opportunities to explain why they chose their methods based on the numbers in an expression. They also analyze the relationship between two numbers in an equation to find an unknown value. Students use what they know about composing units to find unknown three-digit numbers when they are partially covered.

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Warm-Up

Number Talk: Use Sums to Find Sums

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Activity 1: Card Sort: Three-digit Sums

Purpose:

The purpose of this activity is for students to sort addition expressions based on their perceived difficulty. They find the values of expressions they feel are less challenging and expressions they feel are more challenging. Then they compare the methods they use for the expressions they solve with their peers. When sharing, students have opportunities to ask questions about the methods and representations their peers use and suggest methods or representations for expressions that peers may feel are difficult to solve (MP3). When students sort the expressions they look for place value structure to see how they would find the sums (MP7).

Gather:

Base-ten blocks

Copy:

How Did You Do That? Addition Card Sort
Create a set of cards from the blackline master for each group of 2.

Launch:

Groups of 2
Give each group a set of cards.
Give students access to base-ten blocks.

Student Work Time:

“This set of cards includes different expressions. Sort the cards by thinking about whether it would be less challenging or more challenging to find the value of the sum.”
“Make 1 group of sums that you both agree would be less challenging. Make another group of sums that you agree would be more challenging.”
“If you cannot agree on where to place a card, keep it separate from the other groups.”

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Activity 1: Card Sort: Three-digit Sums

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Activity 2: Find the Unknown Value

Purpose:

The purpose of this activity is for students find an unknown addend in sums that have a value of 1,000. They may use what they know about counting by 5, 10, and 100 or use what they know about composing larger units. Although students do not need to know that a thousand is a unit made up of 10 hundreds in grade 2, listen for students who generalize their understanding of place value to make this conjecture to share in the synthesis.

Gather:

Base-ten blocks

Launch:

Groups of 2.
Give students access to base-ten blocks.
Display the image that shows 900 + __0 = 1,000.
“Oh no! Diego spilled paint on his paper and now he can’t see the whole number. What three-digit number do you think is covered up? How do you know?” (100. Because it’s like counting to 1,000 by 100. It would be 900, 1,000.)
30 seconds: quiet think time
1 minute: partner discussion
Share responses.

Student Work Time:

“Now you are going to make sense of a couple more equations where Diego made a mess. Each equation has a part of the three-digit number that is covered up by paint. You’ll work on your own at first, and then have time to share with a partner.”
5 minutes: independent work time
5 minutes: partner work time
Monitor for students who added to find the unknown value for _85 + 615 = 1,000.

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Activity 2: Find the Unknown Value

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Cool-Down: Different Methods for Adding within 1,000

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Image Citations

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