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Adding and Subtracting Fractions
Questions
1. Find the lowest common denominator, then add the fractions
2. Find the lowest common denominator , then add the fractions
3. Combine
4. Combine
5. Combine
6. Combine
7. Combine
8. Combine
1. Technique: prime factor the numerators to determine the LCD (lowest common denominator).
multiply by appropriate
numbers to get common denominator
simplify
now that the denominators are the same , you
can add numerators
simplify
2.
3. The denominators are already the same.
4. The denominators are already the same.
5.
Note: we usually would write 18 = 2 × 9 but since we are
going to cancel everything in the numerator, it helps to write
as 18 = 1 × 2 × 9 so we can see that there will still be a 1 left in the
numerator.
6. First, convert the mixed numbers to improper fractions since we know how to add improper fractions.
Now get a lowest common denominator.
7.
8. First, convert the mixed numbers to improper fractions since we know how to add improper fractions.
Now get a lowest common denominator .
Now we can add.
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