KS3

How to subtract fractions

Part ofMathsFractions

A fraction is made up of two parts. A numerator (the top number) and a denominator (the bottom number).
When we subtract fractions the denominator must be the same.

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Find out how to subtract fractions

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Click here to see a step-by-step slideshow.
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WHAT YOU NEED: A whiteboard, pens, board rubber and a ruler.
$A image showing the fractions 3/5 and 1/4$
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STEP 1 - Draw a square with 5 columns (5 is the denominator of the first fraction) and a square with 4 rows (4 is the denominator of the second fraction).
$An image showing two squares divided into fractions$
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STEP 2 - Colour 3 sections of the first square and 1 section of the second square. These represent ³/₅ and ¹/₄
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STEP 3 - Divide the first square into 4 rows (4 is the denominator of the second fraction).
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STEP 4 - Divide the second square into 5 columns (5 is the denominator of the first fraction). Both squares now contain 20 sections. This is the common denominator.
$Image showing two squares that have been divided into fractions$
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STEP 5 - Count the coloured sections and rewrite the fractions.
$Image showing fractions$
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STEP 6 - The denominator is now the same for both fractions. This is called the common denominator. Subtract 5 from 12, making 7.
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STEP 7 - The answer is ⁷/₂₀ of a mile.

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