Learn to add and subtract fractions with unlike denominators.

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Learn to add and subtract fractions with unlike
denominators.
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Vocabulary
least common denominator (LCD)?
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The Pacific Ocean covers of Earths surface.
The Atlantic Ocean covers of Earths
surface. To find the fraction of Earths surface
that is covered by both oceans, you can add
and , which are unlike fractions.
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To add or subtract unlike fractions, first
rewrite them as equivalent fractions with a
common denominator.
Remember!
Fractions that represent the same value are
equivalent.
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Additional Example 1 Cooking Application Mark
made a pizza with pepperoni covering of
the pizza and onions covering another . What
fraction of the pizza is covered by pepperoni and
onions?

Find a common denominator for 4 and 3 4 x 3
12.
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Additional Example 1 Continued
Write equivalent fractions with 12 as the common
denominator.
Add the numerators. Keep the common denominator.


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The pepperoni and onions cover of the pizza.
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Check It Out Example 1 Tori made a pizza with
peppers covering of the pizza and ham
covering another . What fraction of the pizza
is covered by ham and peppers?
?
Find a common denominator for 3 and 2 3 X 2 6.


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Check It Out Example 1 Continued
Write equivalent fractions with 6 as the common
denominator.
Add the numerators. Keep the common denominator.


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You can use any common denominator or the least
common denominator to add and subtract unlike
fractions. The least common denominator (LCD) is
the least common multiple of the denominators.
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Additional Example 2A Adding and Subtracting
Unlike Fractions Add or subtract. Write each
answer in simplest form. Method 1 Multiplying
denominators.


Multiply the denominators. 10 8 80
Write equivalent fractions with a common
denominator.

Subtract.
Write the answer in simplest form.
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Additional Example 2B Adding and Subtracting
Unlike Fractions Add or subtract. Write each
answer in simplest form. Method 2 Use the LCD.

Multiples of 12 12, 24,
Multiples of 8 8, 16, 24, The LCD is 24.

Write equivalent fractions with a common
denominator.

Subtract.
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Additional Example 2C Adding and Subtracting
Unlike Fractions Add or subtract. Write each
answer in simplest form. Method 3 Use mental
math.

Think 16 is a multiple of 8, so the LCD is 16.


Rewrite with a denominator of 16.

Add.
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Additional Example 2D Adding and Subtracting
Unlike Fractions Add or subtract. Write each
answer in simplest form. Method 3 Use mental
math.

Think 16 is a multiple of 8, so the LCD is 16.



Rewrite with a denominator of 16.
Subtract.
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Check It Out Example 2A Add or subtract. Write
each answer in simplest form. Method 1
Multiplying denominators.
Multiply the denominators. 10 6 60

Write equivalent fractions with a common
denominator.

Subtract.
Write the answer in simplest form.
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Check It Out Example 2B Add or subtract. Write
each answer in simplest form. Method 2 Use the
LCD.
Multiples of 7 7, 14, 21,

Multiples of 3 3, 6, 9, 12, 15, 18, 21, The
LCD is 21.

Write equivalent fractions.
Subtract.
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Check It Out Example 2C Add or subtract. Write
each answer in simplest form. Method 3 Use
mental math.

Think 12 is a multiple of 6, so the LCD is 12.


Rewrite with a denominator of 12.

Add.
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Check It Out Example 2D Add or subtract. Write
each answer in simplest form. Method 3 Use
mental math.

Think 12 is a multiple of 6, so the LCD is 12.


Rewrite with a denominator of 12.

Subtract.