Multiplying and Dividing Fractions

Multiplying and Dividing Fractions

Recall the parts of a fraction:

 $\frac{numerator}{denomiator}$  

When you are multiplying fractions, there are up to two ways to find the correct answer.

First way: multiply the numerator and denominator straight across.

 $\frac{2}{3}\cdot\frac{3}{4}$  = $\frac{6}{12}$  

Then simplify your answer:

 $\frac{6}{12}\ \longrightarrow\ \frac{1}{2}$  

Option 2: "cross reduce" first, or in other words, you divide the diagonals by the same number BEFORE you multiply... then multiply across

Multiple Choice

Try the following: $\frac{3}{5}\cdot\frac{10}{12}$  

•  $\frac{2}{4}$  

•  $\frac{1}{2}$  

•  $\frac{30}{60}$  

•  $\frac{15}{30}$  

Hopefully you got this answer no matter how you solved it!

Multiple Choice

Try again!

 $\frac{6}{7}\cdot\frac{3}{4}$  

•  $\frac{18}{21}$  

•  $\frac{9}{14}$  

•  $\frac{21}{24}$  

•  $\frac{7}{8}$  

Don't forget your rules about negatives:

So when you have this problem, don't forget your rules:

 $-\frac{2}{7}\cdot\frac{14}{15}$  
You have a NEGATIVE x POSITIVE, 
so your answer is...

 $-\frac{4}{15}$  

Multiple Choice

 $-\frac{9}{10}\cdot\left(-\frac{6}{12}\right)$  

•  $-\frac{54}{120}$  

•  $\frac{54}{120}$  

•  $-\frac{9}{20}$  

•  $\frac{9}{20}$  

Hopefully your strategy worked:

Don't forget,

NEGATIVE x NEGATIVE = POSITIVE

Watch the video on the next slide to see it done in real-time. Take notes if you need to!