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Beginning and Intermediate Algebra - Wallace Math Courses ...

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Example 18.<br />

21 28<br />

÷<br />

16 6<br />

21 6<br />

·<br />

16 28<br />

3 3<br />

·<br />

8 4<br />

9<br />

32<br />

Multiply by the reciprocal<br />

Reduce 21 <strong>and</strong> 28 by dividing by 7. Reduce 6 <strong>and</strong> 16 by dividing by 2<br />

Multiply numerators across <strong>and</strong> denominators across<br />

Our Soultion<br />

To add <strong>and</strong> subtract fractions we will first have to find the least common denominator<br />

(LCD). There are several ways to find an LCD. One way is to find the<br />

smallest multiple of the largest denominator that you can also divide the small<br />

denomiator by.<br />

Example 19.<br />

Find the LCD of8<strong>and</strong> 12 Test multiples of 12<br />

12? 12<br />

8<br />

Can ′ 24?<br />

t divide 12 by 8<br />

24<br />

=3<br />

8<br />

24<br />

Yes! We can divide 24 by 8!<br />

Our Soultion<br />

Adding <strong>and</strong> subtracting fractions is identical in process. If both fractions already<br />

have a common denominator we just add or subtract the numerators <strong>and</strong> keep the<br />

denominator.<br />

Example 20.<br />

While 5<br />

4<br />

7 3<br />

+<br />

8 8<br />

10<br />

8<br />

5<br />

4<br />

Same denominator, add numerators7 +3<br />

Reduce answer, dividing by 2<br />

Our Solution<br />

can be written as the mixed number 11 , in algebra we will almost never<br />

4<br />

use mixed numbers. For this reason we will always use the improper fraction, not<br />

the mixed number.<br />

14

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