Unit 2, Lesson 9

Add and Subtract within 100

Grade 2

Warm-up

Which Three Go Together: Tens and Ones

Which 3 go together?

Base ten diagram. 3 tens. 10 ones. The tens do not show each unit of one. — A

Base ten diagram. 4 groups of 10 ones. — C

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Activity 1

Card Sort: Sort and Find the Value

Your teacher will give you a set of cards that show expressions and diagrams.

Match each expression to a diagram. Be ready to explain your reasoning.
Choose 1 addition expression. Find the value of the sum.
Choose 1 subtraction expression. Find value of the difference.

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Activity 2

Add or Subtract

Find the value of each expression. Show your thinking using objects, drawings, numbers, or words.

Student Section Summary

We added two-digit numbers. We composed 1 ten by putting 10 ones together. We also subtracted two-digit numbers. We decomposed 1 ten by breaking it apart into 10 ones. We used base-ten blocks and base-ten diagrams to show our thinking.

<p>Base ten diagram. 6 tens, and 3 ones. 2 tens crossed out and the 3 ones, crossed out. One of the crossed out tens has an arrow pointing to a circle with10 ones inside. 5 ones in the circle are crossed out. </p>

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Lesson 9

Add and Subtract within 100

Warm-up

Which Three Go Together: Tens and Ones

Are You Ready for More?

Activity 1

Card Sort: Sort and Find the Value

Are You Ready for More?

Activity 2

Add or Subtract

Student Section Summary

Have feedback on the curriculum?

Are You Ready for More?

Standards Alignment

Building On

Addressing

Building Toward

2.NBT.5

Standards Alignment

Building On

Addressing

2.NBT.5

Building Toward

Standards Alignment

Building On

Addressing

2.NBT.5

Building Toward