Adding & Subtracting Fractions

Adding & Subtracting Mixed Numbers

Review adding & subtracting fractions

Fractions must ALWAYS be simplified!

To find the least common denominator, you have to find the smallest number that both denominators will go into evenly.

For example:

2 and 3 both go into 6.

4 and 5 both go into 20.

6 and 9 both go into 18.

6 and 9 would also both go into 54,

but 18 is much smaller and easier to work with.

One of the Math Antics videos you watched showed how to find the LEAST common denominator. If you don't feel confident with this skill, go rewatch the video. In the following slides, you will practice finding the LEAST common denominator.

Multiple Choice

In order to add or subtract fractions, you must have

• a common denominator.

• more than 3 numbers.

• a greatest common factor.

• an IQ of 180.

Fill in the Blank

What is the LEAST common denominator of these fractions?

 $\frac{1}{3},\ \frac{1}{4}$  

Fill in the Blank

What is the LEAST common denominator of these fractions?

 $\frac{1}{8},\ \frac{3}{4}$  

Fill in the Blank

What is the LEAST common denominator of these fractions?

 $\frac{7}{8},\ \frac{5}{6}$  

Fractions must ALWAYS be simplified!

Once you have found the least common denominator, you need to create equivalent fractions. Look at the examples on the next slide.

 $\frac{2}{3},\ \frac{5}{8}$  

The common denominator is 24.

 $\frac{2}{3}\times\ \frac{ }{?\ }=\ \frac{ }{24}$  


 $\frac{5}{8}\times\ \frac{ }{?}=\ \frac{ }{24}$  

You have to think what you would
multiply each denominator by to get 24.

Whatever you multiply the denominator by, you have to multiply the numerator by the same thing.

 $\frac{2}{3}\times\frac{8}{8}=\frac{16}{24}$  

 $\frac{5}{8}\times\frac{3}{3}=\frac{15}{24}$  

Fractions must ALWAYS be simplified!

Multiple Choice

Which fraction is equivalent to $\frac{4}{5}$ ? 

•  $\frac{4}{20}$  

•  $\frac{16}{20}$  

•  $\frac{5}{20}$  

•  $\frac{12}{20}$  

Multiple Choice

Which fraction is equivalent to $\frac{3}{7}$ ? 

•  $\frac{12}{28}$  

•  $\frac{12}{21}$  

•  $\frac{10}{14}$  

•  $\frac{17}{21}$  

Fractions must ALWAYS be simplified!

Once you have created equivalent fractions with a common denominator, you are ready to add or subtract.

Add or subtract the numerators. Keep the common denominator!

Simplify if needed.

Fill in the Blank

 $\frac{5}{6}+\frac{3}{4}$  

Fill in the Blank

 $\frac{3}{5}+\frac{1}{3}$  

Fill in the Blank

 $\frac{5}{6}-\frac{1}{4}$  

Fill in the Blank

 $\frac{7}{8}-\frac{1}{5}$  

How to add mixed numbers:

1. Find the LEAST common denominator.

2. Create equivalent fractions using the LEAST common denominator.

3. Add the fractions.

4. Change to a mixed number, if needed.

5. Add the whole numbers.

Fractions must ALWAYS be simplified!

Fill in the Blank

 $1\frac{2}{3}+3\frac{3}{5}$  

Fill in the Blank

 $6\frac{1}{4}+3\frac{2}{5}$  

How to subtract mixed numbers:

1. Find the LEAST common denominator.

2. Create equivalent fractions using the LEAST common denominator.

3. Subtract the fractions.

4. Subtract the whole numbers.

Fractions must ALWAYS be simplified!

Fill in the Blank

 $7\frac{5}{6}-2\frac{1}{4}$  

Fill in the Blank

 $10\frac{4}{5}-4\frac{1}{8}$  

Fill in the Blank

 $8\frac{3}{4}-2\frac{3}{10}$