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3.08 Multiplication with up to 2 digits

Lesson

Are you ready?

We can multiply numbers by larger numbers, once we've mastered multiplying by single digit numbers.

Find $5296\times4$5296×4.

Vocabulary:
  • Another word that we can use to describe the ones place is 'units'.

  • You might notice that sometimes the standard algorithm is called the 'vertical algorithm'. Let's think about why. When we use the standard algorithm, we line our numbers up in 'vertical' place value columns.

Learn

Let's see how to multiply a $2$2 digit number by another $2$2 digit number.

Apply

Question 1

Let's use the area model to find $28\times55$28×55.

  1. Fill in the areas of each rectangle.

                $25$25               $3$3
    $50$50           $\editable{}$               $\editable{}$    
                               
    $5$5           $\editable{}$               $\editable{}$    
                               
  2. Find the sums of each column

                $25$25               $3$3
    $50$50           $1250$1250               $150$150    
                               
    $5$5           $125$125               $15$15    
                               
    Total:           $\editable{}$               $\editable{}$    
                               
  3. What is the total area of the rectangles?

                $25$25               $3$3    
    $55$55           $1375$1375               $165$165    
     
     
     
  4. So what is $28\times55$28×55?

Remember!

Using a standard algorithm means we can multiply larger numbers the same way, just with more steps. Once we know how to solve problems this way, there's no limit to how big the numbers could be!

 

Outcomes

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.

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