Multiplying and Dividing Fractions

Multiplying and Dividing Fractions

Multiplying Fractions

This is the easy one. If fact, you've already done it when you were adding fractions and finding a common denominator.

When multiplying fractions, just multiply straight across. Numerator times numerator. Denominator times denominator. That's it.

Multiple Choice

 $\frac{1}{2}\times\frac{4}{5}$  

•  $\frac{4}{10}$  

•  $\frac{5}{7}$  

Multiple Choice

 $\frac{3}{5}\left(\frac{2}{3}\right)$  

•  $\frac{5}{8}$  

•  $\frac{6}{15}$  

Multiple Choice

 $\frac{1}{2}\left(\frac{1}{2}\right)$  

•  $\frac{1}{2}$  

•  $\frac{1}{4}$  

•  $\frac{2}{4}$  

Multiple Choice

What's the rule for multiplying fractions?

• Just multiply straight across.

• Keep, Change, Flip

• You must have a common denominator

Poll

How do you feel about multiplying fractions?

• Great (it's pretty easy)

• Horrible (I'm so lost)

• Eh... it's okay.

Dividing Fractions

Rule#1 for Dividing Fractions: DON'T DIVIDE.

Instead of dividing you do this procedure:

KEEP, CHANGE, FLIP

Dividing Fractions

So lets look closely at this:

 $\frac{2}{3}\div\frac{4}{5}$  Don't divide. Instead, keep

 the  $\frac{2}{3}$  , change the  $\div$   to   $\times$   

and flip the  $\frac{4}{5}$   so that it's  $\frac{5}{4}$  .

Now just multiply.  $\frac{2}{3}\times\frac{5}{4}=\frac{10}{12}$  

Multiple Choice

After I "Keep, Change, Flip" what equation would I have?

 $\frac{1}{2}\div\frac{2}{5}$  

•  $\frac{2}{1}\times\frac{2}{5}$  

•  $\frac{1}{2}\times\frac{5}{2}$  

Multiple Choice

Solve

 $\frac{1}{2}\div\frac{2}{5}$  

•  $\frac{4}{5}$  
  

•  $\frac{5}{4}$  

•  $\frac{2}{10}$  

Multiple Choice

Solve:

 $\frac{1}{10}\div\frac{2}{3}$  

•  $\frac{3}{20}$  

•  $\frac{2}{30}$  

Multiple Choice

Solve

 $\frac{3}{4}\div\frac{1}{2}$  

•  $\frac{5}{4}$  

•  $\frac{3}{8}$  

•  $\frac{6}{4}$  

Multiple Choice

When dividing fractions, what rule do we use?

• Keep, Change, Flip

• Multiply straight across

• Must have a common denominator