Rounding, Addition, and Subtraction

Lesson 5

Math

Unit 1

3rd Grade

Lesson 5 of 14

Objective


Round three-digit numbers to the nearest hundred using a number line.

Common Core Standards


Core Standards

  • 3.NBT.A.1 — Use place value understanding to round whole numbers to the nearest 10 or 100.

Foundational Standards

  • 2.MD.B.6
  • 2.NBT.A.1

Criteria for Success


  1. Round three-digit numbers to the nearest hundred using a number line if it is helpful.
  2. Understand that, by convention, a number at the midpoint between two benchmarks is rounded to the larger of the two benchmarks.
  3. Use the $$\approx$$ symbol to record estimations.

Tips for Teachers


  • You’ll want to avoid using terms like "round up" and "round down", since these terms can be confusing for students. "Rounding up" a number results in a change in the value of the place to which you’re rounding, where "rounding down" does not. Often students will change the value mistakenly as a result.
  • Criteria for Success #1—4 are all spiraled from Lesson #4.
  • Before the Problem Set, you could have students play "Take Your Places" from Building Conceptual Understanding and Fluency Through Games by the Public Schools of North Carolina.
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Anchor Tasks


Problem 1

Which hundred is 160 closest to on the number line? Plot 100 and 200 on the two endpoints on the number line below. Then plot 160 to prove your answer.

Guiding Questions

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References

Illustrative Mathematics Rounding on the Number Line

Rounding on the Number Line, accessed on Sept. 11, 2017, 8:36 p.m., is licensed by Illustrative Mathematics under either the CC BY 4.0 or CC BY-NC-SA 4.0. For further information, contact Illustrative Mathematics.

Modified by Fishtank Learning, Inc.

Problem 2

a.   Round each of the following numbers to the nearest hundred, using a number line if it would help you. Record your answer using the ≈ symbol.

  1. 432
  2. 387
  3. 64
  4. 21

b.   Batyr is trying to round the number 650 to the nearest hundred. He says, "650 is not closer to 600 or 700, so it cannot be rounded to the nearest hundred." Do you agree with Batyr? Explain your reasoning. 

Guiding Questions

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References

EngageNY Mathematics Grade 3 Mathematics > Module 2 > Topic C > Lesson 14Concept Development, Part 1

Grade 3 Mathematics > Module 2 > Topic C > Lesson 14 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

Modified by Fishtank Learning, Inc.

Problem Set


Answer Keys

Unlock the answer keys for this lesson's problem set and extra practice problems to save time and support student learning.

Discussion of Problem Set

  • Let’s look at #1e. I don’t think 972 can round to 1,000 since that is the number rounded to the nearest thousand, not hundred. Do you agree or disagree? Why?
  • Let’s look at #1f. How did you decide how to round 250? Why? 
  • Let’s look at #3. Which values would round to 600? Can you think of other values that would round to 600? What are all of the possibilities?
  • Let’s look at #4. Is Christian or Alexis correct? How do you know?

Target Task


Round each of the following numbers to the nearest hundred. Show or explain your thinking.

a.   $$750 \approx$$ __________

b.   $$135 \approx$$ __________

c.   $$84 \approx$$ __________

Student Response

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Additional Practice


The Extra Practice Problems can be used as additional practice for homework, during an intervention block, etc. Daily Word Problems and Fluency Activities are aligned to the content of the unit but not necessarily to the lesson objective, therefore feel free to use them anytime during your school day.

Extra Practice Problems

Answer Keys

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Word Problems and Fluency Activities

Word Problems and Fluency Activities

Help students strengthen their application and fluency skills with daily word problem practice and content-aligned fluency activities.

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Lesson 4

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Lesson 6

Lesson Map

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Topic A: Foundations of Place Value

Topic B: Rounding to the Nearest Ten and Hundred

Topic C: Addition and Subtraction Within 1,000

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