SUBTRACTING FRACTIONS WITH DIFFERENT DENOMINATORS

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SUBTRACTING FRACTIONS WITH DIFFERENT DENOMINATORS

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Back to the Basics

• Subtracting fractions with different denominators
  is much like adding fractions with different
  denominators.
• You cannot subtract the numbers until the
  denominators are the same.
• Lets use Mary and an example.

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• She has 12 apples and puts 8 of them into a
  separate pile.
• Now she wants to take ½ of the apples in the pile
  of 8 and put them into a third pile.
• You want to know what fraction of all the apples
  total will be left in the second if she takes ½
  of that pile away.
• Her equation looks like this
• 8/12 1/2 ?

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• The two fractions cannot be subtracted until the
  denominators are the same.
• You must find the Least Common Denominator (LCD)
  of 12 and 2.
• Since 2 already goes into 12 then 12 is the LCD.
• Because 12 does not change you do not need to
  multiply it by anything before you subtract it.
• But ½ does need to be multiplied before anything
  else can be done.

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• 2 must be multiplied by 6 to get 12.
• So, 1/2 must be multiplied by 6/6.
• 1/2 X 6/6 6/12
• Now you can subtract 6/12 from 8/12.
• 8/12 6/12 2/12
• So, 2/12 (or 1/6 if you simplify it) of the total
  number of apples is left in the second pile.
• Always remember that the denominator must be the
  same before you can subtract any fractions.