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Unit 2

Compare Methods for Subtraction

Lesson 6

Adding and Subtracting within 100

Expressions and Equations

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Let’s compare subtraction methods.

Unit 2 ● Lesson 6

Learning

Goal

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How many Tens? How many Ones?

Unit 2 ● Lesson 6 ● Warm-up

Decide if each statement is true or false. Be prepared to explain your reasoning.

  • 64 = 60 + 4
  • 64 = 50 + 14
  • 64 = 30 + 24

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True or False

Slides are CC BY NC Kendall Hunt Publishing. Curriculum excerpts are CC BY Illustrative Mathematics.

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How many Tens? How many Ones?

Unit 2 ● Lesson 6 ● Warm-up

If we wanted to take-away 9 from 64, which representation would be better? Why?

60 + 4

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50 + 14

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Activity Synthesis

Slides are CC BY NC Kendall Hunt Publishing. Curriculum excerpts are CC BY Illustrative Mathematics.

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Different Ways to Decompose

Unit 2 ● Lesson 6 ● Activity 1

Diego and Elena drew base-ten diagrams to find the value of 82 – 9.

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  1. Compare Diego’s work to Elena’s.
    1. What is the same?
    2. What is different?

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Diego

Elena

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Launch

Slides are CC BY NC Kendall Hunt Publishing. Curriculum excerpts are CC BY Illustrative Mathematics.

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Different Ways to Decompose

Unit 2 ● Lesson 6 ● Activity 1

  1. Tyler used equations to show his thinking.

82 – 9

82 = 70 + 12

12 – 9 = 3

70 + 3 = 73

Diego says Tyler’s work matches his diagram.

Elena says Tyler’s work matches her diagram.

Who do you agree with? Explain.

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Slides are CC BY NC Kendall Hunt Publishing. Curriculum excerpts are CC BY Illustrative Mathematics.

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Different Ways to Decompose

Unit 2 ● Lesson 6 ● Activity 1

  • Diego, Elena, and Tyler saw they needed more ones before they could subtract ones from ones. They showed decomposing a ten in different ways.
  • Here are some of the words we used to describe subtracting by place.
  • Are there any other words or phrases that are important to include on our display?

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Activity Synthesis

Slides are CC BY NC Kendall Hunt Publishing. Curriculum excerpts are CC BY Illustrative Mathematics.

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Introduce Target Numbers, Subtract Tens or Ones

Unit 2 ● Lesson 6 ● Activity 2

  • We are going to learn a new way to play Target Numbers. You and your partner will start with 99 and race to see who can get as closest to 0.
  • First, represent 99 with base-ten blocks.
  • When it’s your turn, draw a card. Decide whether you want to subtract that many tens or that many ones.
  • Then show the subtraction with your blocks and write an equation on your recording sheet.
  • Take turns drawing a card and subtracting until you play 6 rounds or one player reaches 0. After 6 rounds, whoever is closest to 0 is the winner.

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Launch

Slides are CC BY NC Kendall Hunt Publishing. Curriculum excerpts are CC BY Illustrative Mathematics.

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Introduce Target Numbers, Subtract Tens or Ones

Unit 2 ● Lesson 6 ● Activity 2

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Launch

Slides are CC BY NC Kendall Hunt Publishing. Curriculum excerpts are CC BY Illustrative Mathematics.

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Introduce Target Numbers, Subtract Tens or Ones

Unit 2 ● Lesson 6 ● Activity 2

What is the same and what is different about how the ten was decomposed in each of these examples?

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Activity Synthesis

Slides are CC BY NC Kendall Hunt Publishing. Curriculum excerpts are CC BY Illustrative Mathematics.

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Compare Methods for Subtraction

Unit 2 ● Lesson 6

  • Today we compared methods for subtracting and representations for showing our thinking when subtracting.
  • What are different methods you could use to find the value of 50 – 7?

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Lesson Synthesis

Slides are CC BY NC Kendall Hunt Publishing. Curriculum excerpts are CC BY Illustrative Mathematics.

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Mai’s Method

Unit 2 ● Lesson 6

Mai was asked to find the difference for 52 – 7. She started, but she got stuck. Finish Mai’s method.

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Cool-down

Slides are CC BY NC Kendall Hunt Publishing. Curriculum excerpts are CC BY Illustrative Mathematics.

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Slides are CC BY NC Kendall Hunt Publishing. Curriculum excerpts are CC BY Illustrative Mathematics.