Multiplication and Division of Whole Numbers

Lesson 10

Math

Unit 2

5th Grade

Lesson 10 of 20

Objective


Multiply multi-digit numbers and assess the reasonableness of the product.

Common Core Standards


Core Standards

  • 5.NBT.B.5 — Fluently multiply multi-digit whole numbers using the standard algorithm.

Foundational Standards

  • 4.NBT.B.4
  • 4.NBT.B.5
  • 5.NBT.A.1
  • 5.NBT.A.2

Criteria for Success


  1. Compute up to four-digit by two-digit and three-digit by three-digit products using the standard algorithm.  
  2. Predict whether estimated products will be greater than or less than the actual products, based on how the factors were rounded. (Optional)
  3. Assess the reasonableness of an answer by comparing the actual product to the estimated product (MP.1).
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Anchor Tasks

25-30 minutes


Problem 1

Use the digits 1 to 9, at most one time each, to create two numbers that have a product as close to 500,000 as possible. 

You may use any length of factors as you would need, for example, eight-digit by one-digit or four-digit by three-digit.

Guiding Questions

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Student Response

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References

Open Middle Multiplication of Large Numbers

Multiplication of Large Numbers by is made available on Open Middle under the CC BY-NC-SA 4.0 license. Accessed Dec. 7, 2018, 1:04 p.m..

Modified by Fishtank Learning, Inc.

Problem 2

Solve. Then estimate to assess the reasonableness of your answer. Then explain why your estimated product was greater or less than your actual product.  

a.   $$​   714 \times236$$

b.   $$​ 296 \times2,818$$

c.   $$​ 4,002 \times498$$

Guiding Questions

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Student Response

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Problem Set

15-20 minutes


Discussion of Problem Set

  • What is the benefit of estimating before solving?
  • Look at #1b and #1c. What do you notice about the estimated products? Analyze why the estimates are the same yet the products are so different. (You might point out the same issue in #1e and 1f.)
  • How could the cost of the chairs have been found using mental math? 
  • In #3, Carmella estimated that she had 3,000 cards. How did she most likely round her factors?
  • Would rounding the number of boxes of cards to 20 have been a better choice? Why or why not? 
  • Do we always have to round to a multiple of 10, 100, or 1,000? Is there a number between 10 and 20 that would have been a better choice for Carmella?
  • Can you identify a situation in a real-life example where overestimating would be most appropriate?
  • Can you identify a situation in the real world where underestimating would be most appropriate? 

Target Task

5-10 minutes


Problem 1

For parts (a) and (b) below,

  • Solve. Show or explain your work.
  • Assess the reasonableness of your answer.

a.   910 × 233

b.   852 × 488

Student Response

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Problem 2

Damian’s work on a multiplication problem is shown below.

a.   Why is Damian’s answer not reasonable? Use estimation in your explanation. 

b.   What mistake do you think Damian made? Why do you think he made that mistake?

c.   Find the correct product of 5,126 × 47.

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

Divide multiples of powers of ten by multiples of ten without remainders. Estimate multi-digit quotients by rounding numbers to their largest place value.

Lesson 11
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Lesson Map

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

Topic A: Writing and Interpreting Numerical Expressions

Topic B: Multi-Digit Whole Number Multiplication

Topic C: Multi-Digit Whole Number Division

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