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Recap:
All fractions have a numerator and a denominator.
The first step in subtracting 2 fractions is to check if both denominators are the same number (like denominators) or different numbers (unlike denominators).
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Fractions whose denominators are the same are the easiest to subtract. You just need to subtract the numerators and leave the denominator unchanged.
Example: ![]() |
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More:
When fractions have different denominators, we have to change them so they both have the same denominator.
We do this by finding the lowest common multiple of the 2 numbers. We use equivalent fractions.
Example:
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In this example, the denominators are 3 and 2. |
Step 1: We write out the first few multiples (Times Tables) of 3 and 2. We see that 6 is the smallest number that occurs in both tables (lowest common multiple). |
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Step 2:
We can now change both fractions so that they have the same denominator. We are changing each fraction to its equivalent fraction.
6 is the second multiple of 3 so we need to multiply both the numerator as well as the denominator by 2. |
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6 is the third multiple of 2 so we need to multiply both the numerator as well as denominator by 3. |
Let's put it all together.
Here is an alternative way to look at it:
We cannot subtract the fractions with unlike denominators because each portion of the fraction is of a different size. We need to change them to an equal size.
After changing to equivalent fractions:
Each portion of the equivalent fractions is now of an equal size. We can easily subtract 3 portions from 4 portions.
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Next: Subtracting a Fraction From a Mixed Number or a Whole Number