Adding and Subtracting Fractions

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Adding and Subtracting Fractions

• With different denominators

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Different Denominators

• It's easy to add and subtract like fractions, or
  fractions with the same denominator.
• You just add or subtract the numerators and keep
  the same denominator.
• To do this, you need to know how to find the
  least common denominator.
• In an earlier lesson, you learned how to
  simplify, or reduce, a fraction by finding an
  equivalent, or equal, fraction where the
  numerator and denominator have no common factors.
  
• To do this, you divided the numerator and
  denominator by their greatest common factor.

• Next we will learn that you can also multiply the
  numerator and denominator by the same factor to
  make equivalent fractions.

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L C D

• Since only like fractions can be added or
  subtracted, we first have to convert unlike
  fractions to equivalent like fractions.
• We want to find the smallest, or least, common
  denominator, because working with smaller numbers
  makes our calculations easier.
• The least common denominator, or LCD, of two
  fractions is the smallest number that can be
  divided by both denominators.

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Methods for Finding LCD

• The first method is to simply start writing all
  the multiples of both denominators, beginning
  with the numbers themselves. Here's an example of
  this method. Multiples of 4 are 4, 8, 12, 16, and
  so forth (because 1 44, 2 48, 3 412, 4
  416, etc.). The multiples of 6 are 6,
  12,--that's the number we're looking for, 12,
  because it's the first one that appears in both
  lists of multiples. It's the least common
  multiple, which we'll use as our least common
  denominator.

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Adding like Denominators

• Just simply add the top 2 numbers of the
  fractions together since they have common
  denominators.

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Subtracting Like Denominators

• Subtracting like denominators is just as easy as
  adding them! All you have to do is subtract the
  numerators and keep the same common denominator

3/4 1/4 2/4 4/6 - 1/6 3/6 7/9 1/9
6/9 5/9 3/9 2/9
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Adding Unlike Denominators
Find the least common denominator between 12 and
16 which is 48. Then find out what number
times 12 is equal to 48 and do the same for 16
(3). Multiply 3 by both of the numerators, and
then add the fractions!
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Subtracting Unlike Denominators

• The least common denominator between 3 and 12 is
  12
• Find what number times 3 is equal to 12 and then
  multiply that by 1
• Then simply subtract the numerator

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HYPERLINKS

• Visit these websites below to learn more about
  fractions
• http//www.kidsolr.com/math/fractions.html
• http//www.aaamath.com/B/fra.htm
• http//www.aaamath.com/fra410a-addfractld.html

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GAME

• Go to http//www.aaamath.com/fra66l-subfracud.html
  to play the online fraction game!
• Click start and then solve the subtraction
  problem, and then report your score at the end!

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• YOU DID IT! NOW YOU ALL KNOW YOUR FRACTIONS!