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4.01 Finding unknowns


Are you ready?

Remembering your  times tables  will help you solve problems in this lesson. Let's give this problem a try.


Example 1

What is 8\times3?

Worked Solution
Create a strategy

We can think of it as 8 groups of 3.

An array of squares with 8 rows and 3 columns.
Apply the idea

Count the number of squares in the array to get:8\times3=24

Idea summary

We get the same answer whichever way we look at our array.

An image showing an array with 2 columns and 4 rows. Ask your teacher for more infromation.

Find unknowns with multiplication and division

This video shows us how to find unknowns using our multiplication and division facts.

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Example 2

Complete the statement with the missing number: 8\times⬚=80

Worked Solution
Create a strategy

Rewrite the statement as a division statement.

Apply the idea

We can rewrite the statement as 80\div8=⬚.

To find the answer, we can count up by 8's until we get to 80. We can see that we needed to count up 10 times: 8, \, 16, \, 24, \, 32, \, 40, \, 48, \, 56, \, 64, \, 72, \,80. So: 80\div 8=10 Which also means:8\times10=80

Idea summary

We can write multiplication statements as division statements to help find an unknown.

Turn around facts tell us that for multiplication the order doesn't matter. So for something like 4 \times 5, we can also write it as 5 \times 4 and get the same answer.



uses mental and informal written strategies for multiplication and division

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