Adding & Subtracting Fractions Flashcards

All 6 cards in this deck

Which denominator should you use when adding or subtracting fractions with different denominators?
e.g. denominators $5$ and $3$

The lowest common multiple of the denominators.
For $5$ and $3$ this is $15$.

What are the steps to add two fractions with different denominators?
e.g. $\frac{1}{4}+\frac{1}{6}$

1. Find a common denominator: $12$
2. Write equivalent fractions: $\frac{3}{12}+\frac{2}{12}$
3. Add the numerators, keep the denominator: $\frac{5}{12}$

What are the steps to subtract two mixed numbers?
e.g. $3\frac{1}{2}-1\frac{1}{6}$

1. Convert to improper fractions: $\frac{7}{2}-\frac{7}{6}$
2. Use a common denominator: $\frac{21}{6}-\frac{7}{6}=\frac{14}{6}$
3. Simplify and write as a mixed number: $2\frac{1}{3}$

True or false? To add two fractions you add the numerators and add the denominators.

False. You only add the numerators, once the fractions share a common denominator.

True or false? Changing fractions into decimals is a reliable way to get an exact answer to a fraction calculation.

False. Fractions such as $\frac{2}{3}$ give recurring decimals, so decimals may be rounded; work in fractions to be exact.

How do you deal with adding a negative fraction?
e.g. $\frac{1}{5}+\left(-\frac{2}{5}\right)$

Adding a negative fraction is the same as subtracting it.
$\frac{1}{5}-\frac{2}{5}=-\frac{1}{5}$