Adding Fraction With Different Denominator

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Adding Fraction With Different Denominator
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Definition

• Common Denominator When the fractions in an
  addition problem do not have the same
  denominators, rewrite the problem so that each
  fraction has the same denominator.
• Lowest Common Denominator A common denominator
  is a number that can be divided evenly by all the
  denominators in a problem. The smallest number
  that can be divided evenly by all the
  denominators in a problem.
• Sometimes the largest denominator is a problem is
  the lowest common denominator.

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Finding a Common Denominator

• Here are two ways of finding a common denominator
  when the largest denominator in addition problem
  doesnt work.
• Multiply the denominators together.
• Go through the multiplication table of the
  largest denominator.

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Example 1

• 2/5 3/4
• Multiply the denominators. 5 X 4 20. 20 is the
  lowest common denominator (LCD).
• Raise each fraction to 20ths .
• Add the new fractions.
• Change the answer to a mixed number.

• 2/5 8/20
• 3/4 15/20
• 23/20 1 3/20

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Example2

• 2/3 5/6 3/4
• Go through the multiplication table of the 6.
• 6 x 1 6, which cannot be divided by 4.
• 6 x 2 12, which can be divided by 3 and 4.
• Raise each fraction to 12ths.
• Add the new fractions.
• Change the answer to a mixed number and reduce.

• 2/3 8/12
• 5/6 10/12
• 3/4 9/12
• 27/12 2 3/12
• 2 1/4

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Practice

• 3/5 2/3
• 3/7 1/3
• 1/4 3/5 7/10

• 2/3 4/9 5/6
• 4 3/5 6 ¾
• 6 5/12 7 3/8