Rounding, Addition, and Subtraction

Lesson 4

Math

Unit 1

3rd Grade

Lesson 4 of 14

Objective


Define estimation and its purpose. Round two-digit numbers to the nearest ten 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. Understand estimation/approximation as the process of using values that are close enough to the right value to make calculating easier.
  2. Understand rounding as a type of estimation in which a close benchmark number is used instead of an exact one. 
  3. Understand that the terms "near" or "close" imply the use of an estimate. 
  4. Round two-digit numbers to the nearest ten using a number line.
  5. 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. 
  • In some curricula and standardized tests, 3.NBT.1 is interpreted to mean students should be able to round any number to the nearest ten or hundred, not just numbers in the hundreds. However, given that children have not yet built place value understanding for numbers beyond 1,000 yet and Bill McCallum notes on his blog Mathematical Musings that this is a reasonable interpretation, students are only expected to round numbers less than 1,000 in this series of lessons. 
  • Before the Problem Set, you could have students play "Rounding to the Tens/Hundreds Showdown" from Building Conceptual Understanding and Fluency Through Games by the Public Schools of North Carolina.
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Anchor Tasks

25-30 minutes


Problem 1

The number 16 lies between 10 and 20 on the number line. Label all the other tick marks between 10 and 20. Is 16 closer to 10 or 20 on the number line?

Guiding Questions

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Student Response

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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.   Rosie is rounding 74 to the nearest ten. She draws the following number line to help her:

  1. Why do you think Rosie made a number line from 70 to 80 with just 75 marked? 
  2. What is 74 rounded to the nearest ten?

b.   Round each of the following numbers to the nearest ten, using a number line if it would help you. Record your answer using the $$\approx$$ symbol.

  1. 58
  2. 32
  3. 97

Guiding Questions

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Student Response

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Problem Set

15-20 minutes


Discussion of Problem Set

  • Why is a number line a good tool to use for rounding?
  • How does labeling the halfway point help you to round?
  • What are some real-world situations where it would be useful to round and estimate?

Target Task

5-10 minutes


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

a.   $$46 \approx$$ __________

b.   $$24 \approx$$ __________

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.

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.

Next

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

Lesson 5
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Lesson Map

A7CB09C2-D12F-4F55-80DB-37298FF0A765

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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