Multi-Digit Multiplication

Lesson 17

Objective

Multiply two-digit multiples of 10 by two-digit numbers.

Common Core Standards

Core Standards

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  • 4.NBT.B.5 — Multiply a whole number of up to four digits by a one-digit whole number, and multiply two two-digit numbers, using strategies based on place value and the properties of operations. Illustrate and explain the calculation by using equations, rectangular arrays, and/or area models.

Foundational Standards

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  • 3.NBT.A.3

  • 4.NBT.A.1

  • 4.NBT.B.4

  • 3.OA.B.5

  • 3.OA.C.7

Criteria for Success

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  1.  Multiply multiples of 10 by two-digit numbers by decomposing the multiply of 10 and using the associative property (e.g., 80 x 34 = 8 x 10 x 34 = 340 x 8 or 272 x 10).
  2. Multiply multiples of 10 by two-digit numbers by decomposing the two-digit number and using the distributive property (e.g., 80 x 34 = (80 x 30) + (80 x 4) = 2,400 + 320 = 2,720).

Tips for Teachers

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Remote Learning Guidance

If you need to adapt or shorten this lesson for remote learning, we suggest prioritizing Anchor Task 1 and Anchor Task 2 (benefit from discussion). Find more guidance on adapting our math curriculum for remote learning here.

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Anchor Tasks

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Problem 1

Two different students solved the problem 40 x 22 below. Study their work and determine whether the strategy they used works.

Guiding Questions

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Problem 2

Yet another student solved $$40 \times 22$$ with a different strategy below. Study their work and determine whether the strategy they used works. 

Guiding Questions

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Problem 3

Estimate each product. Then use any method to solve. 

a. 60 x 31

b. 18 x 70

c. 90 x 56

d. 35 x 80

Guiding Questions

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Problem Set & Homework

Discussion of Problem Set

  • How is #1a of the Problem Set less complex than the others?
  • How could you have used #3b to solve #4b? 
  • How could you have used #3c to solve #4c?
  • Can you explain why #4c and #4d have the same product?
  • When we record partial products, do we have to start with the one with the smallest place value? Will we get a different result if we start with the tens?
  • When we multiply by a multiple of 10, why is there always a 0 in the ones place?

Target Task

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Problem 1

Which of these expressions can be used to find the product 20 x 41? Select the two correct answers. 

A.      41 x 10 + 2

B.      41 x 2 x 10

C.      (40 + 20) x (1 + 20)

D.       20 x 40 + 1

E.        41 x 2 x 10

F.        (20 x 40) + (20 x 1)

Problem 2

Solve. Show or explain your work. 

32 x 60

Mastery Response

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Additional Practice

Unit Practice

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