Curriculum  /  Math  /  3rd Grade  /  Unit 1: Rounding, Addition, and Subtraction  /  Lesson 7

Rounding, Addition, and Subtraction

Lesson 7

Math

Unit 1

3rd Grade

Lesson 7 of 14

Objective

Round multi-digit numbers to any place in more complex cases, including those involving real-world contexts and/or assessing the reasonableness of that estimate.

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 that the term "about" implies the use of an estimate.
  2. Understand the advantages and disadvantages of rounding a value to various places, including the precision of rounding a number to a smaller place (MP.6) and ease of working/operating when rounding a number to a larger place.
  3. Understand that an estimate is reasonable if it makes sense and/or is fair in the context of the problem.
  4. Determine the most appropriate place to round to in order to have a reasonable estimate, based on the context of the problem (MP.1, MP.3).
  5. Reason about the possible numbers that could have been rounded to a certain value.

Tips for Teachers

  • This whole lesson provides an excellent opportunity for students to construct viable arguments and critique the reasoning of others regarding when to round and to what level of precision, based on the context of the problem (MP.3). "How close an estimate must be to the actual computation is a matter of context," and thus "the goal of computational estimation is to be able to flexibly and quickly produce an approximate result that will work for the situation and give a sense of reasonableness" (Van de Walle, p. 195). Thus, these tasks offer an opportunity for a rich discussion where one’s decision about the degree of precision of an estimate should be supported by reasoning.  
  • 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.
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Anchor Tasks

25-30 minutes

Problem 1

A coat costs $92. Mrs. Ingall says the coat is about $90. Mr. Silver says it is about $100. Who is correct, Mrs. Ingall, Mr. Silver, both of them, or neither of them? Explain your answer.

Guiding Questions

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Student Response

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Problem 2

When a number is rounded to the nearest ten, it rounds to the lesser benchmark. When a number is rounded to the nearest hundred, it rounds to the greater benchmark. What might the number be?

Guiding Questions

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Student Response

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Problem Set

15-20 minutes

Discussion of Problem Set

  • Look at #2. What do you notice about the numbers that when rounded to the nearest ten would round to 100? What about when rounded to the nearest hundred?  
  • Look at #5a. Is she correct? How do you know?
  • Look at #5b. Is she correct? How do you know? How is this different from #5a? 
  • Look at #6. Whose method do you think is correct? Why?

Target Task

5-10 minutes

Ms. Needham knows there are 283 students in Grades 3, 4, and 5 at Fishtank Learning Elementary School. She says that there are about 280 students. 

a.   Did Ms. Needham round to the nearest ten or hundred?

b.   Ms. Needham rounded the number of Grade 3, 4, and 5 students to be able to set up seats in the gym for an assembly with those grades. Do you think Ms. Needham made a good decision about how she rounded the number of students? Why or why not?

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

Add numbers with up to one composition within 1,000.

Lesson 8
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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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