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5.03 Easily relatable denominators


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Identifying numbers that are  multiples of other numbers  is very useful when we work with fractions.


Example 1

True or False: 18 is a multiple of 3.

Worked Solution
Create a strategy

List multiples of 3.

Apply the idea

Using your times tables or skip counting we can find the first 8 multiples of 3: 3, \,6, \,9, \,12, \,15, \,18, \,21, \,24

Since 18 is in this list, 18 is a multiple of 3. This means the statement is true.

Idea summary

Factors and multiples are related to multiplication facts. Writing out a multiplication problem, such as 4\times 6=24 can help us remember which is which.

Find common denominators

This video shows us how to find equivalent fractions so that we end up with common denominators.

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Example 3

Find the equivalent fraction:\dfrac{3\times 2}{5\times 2}=\dfrac{6}{⬚}

Worked Solution
Create a strategy

Multiply the denominator by the same number that has been multiplied by the numerator.

Apply the idea

The numerator has been multiplied by 2, so we must multiply the denominator by 2:

\displaystyle \dfrac{3\times 2}{5\times 2}\displaystyle =\displaystyle \dfrac{6}{10}Multiply 5 by 2
Idea summary

To find an equivalent fraction, we must multiply the denominator and numerator by the same number.



Solve problems involving addition and subtraction of fractions with the same or related denominators

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