Adding and Subtracting Fractions

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Adding and Subtracting Fractions

• By Jimmy Quinlan

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Adding Fractions with common denominators
Adding and subtracting fractions with common (the
same) denominators (bottom number) is easy to do!
Simply add or subtract the numerators (top
number) depending on the operation. Remember the
denominator always stays the same!
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Adding Fractions with different denominators
Problem You cant add fractions with different
denominators without getting them ready first.
They will be ready to add when they have common
denominators (bottom numbers must be the same).
Solution Turn fractions into equivalent
fractions with a common denominator! This means
that you need to find the Lowest Common Multiple
(LCM) of the two denominators!
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Finding the Lowest Common Denominator(Option
1)

• The lowest common multiple (LCM) of two numbers
  is the lowest number in BOTH lists of multiples.

Multiples of 2 are 2, 4, 6, 8, 10 Multiples of
3 are 3, 6, 9, 12, What is the lowest
common multiple?
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Finding the Lowest Common Denominator(Option
2)

• The lowest common multiple of two numbers is the
  lowest number they will BOTH divide into

2 divides into 2, 4, 6, 8.. 3 divides into 3, 6,
9. What is the lowest number 2 and 3 both
divide into?
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You cant add fractions with different
denominators

The Lowest Common Multiple of 2 and 3 is 6 so
turn all fractions into sixths
Special form of 1
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Lowest common denominator is 10 so make all
fractions tenths
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Turn both fractions into twelfths