how to multiply and divide fractions

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HOW TO MULTIPLY AND DIVIDE FRACTIONS By Frank Wang

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How to Multiply and Divide Fractions. By Frank Wang. Multiplication and Division With Fractions. You know adding and subtracting fractions, right? - PowerPoint PPT Presentation

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Page 1: How to Multiply and Divide Fractions

HOW TO MULTIPLY AND DIVIDE FRACTIONSBy Frank Wang

Page 2: How to Multiply and Divide Fractions

MULTIPLICATION AND DIVISION WITH FRACTIONS

You know adding and subtracting fractions, right?

This PowerPoint is about the other two operations: multiplication and division! Although it is very hard to show it with real life items, it is very simple with regular numbers.

Page 3: How to Multiply and Divide Fractions

PART ONE:

Page 4: How to Multiply and Divide Fractions

MULTIPLICATION

Here is a rule for whole number multiplication: the product of the two numbers will be greater than the two factors. Well, multiplication with fractions is the complete OPPOSITE of that rule.

When you multiply fractions, the product is LESS than the two factors. This happens because a fraction is LESS than one, and anything multiplied by one is itself.

Page 5: How to Multiply and Divide Fractions

HOW TO

This is very easy. There are only two steps to multiplying fractions. First, Multiply the numerators together and multiply the denominators together.

Page 6: How to Multiply and Divide Fractions

STEP 1 EXAMPLE

4/6 x 7/8 = ?

4x7= 286x8= 48 ANSWER: 28/48

Page 7: How to Multiply and Divide Fractions

STEP 2 EXAMPLE

So, your answer is 28/48, right? NO! You have to simplify the fraction. To do this, you have to first find the GCF*.

28: 4, 7, 28, 1, 2, 1448: 6, 8, 48, 1, 2, 24, 4, 12, 16, 3

*If 1 is the GCF, it is already in simplest form!

Page 8: How to Multiply and Divide Fractions

GCF

After that, divide the numerator and the denominator by the GCF.

28 ÷ 4 = 748 ÷ 4 = 12

So, the answer is 7/12.

Page 9: How to Multiply and Divide Fractions

CHECKING

To check if you did this step correctly or not, see if the numerator and denominator still have a common GCF. Let’s say when I wrote out the factors, I didn’t realize that 4 was there, so I chose 2. I would have gotten 14/24. I would then list the factors of these two numbers to check.

14: 7,2,1,1424: 6, 4, 8, 3, 12, 2, 24, 1

14 ÷ 2 = 7 24 ÷ 2 = 12So, the answer is 7/12.

Page 10: How to Multiply and Divide Fractions

PART 2:

Page 11: How to Multiply and Divide Fractions

DIVISION

For dividing whole numbers, the quotient is less than the dividend and divisor. Well, if you do it with fractions, the quotient is greater than the dividend and divisor. This is because of the reason that the multiplication works.

Page 12: How to Multiply and Divide Fractions

HOW TO

Division is pretty much the same as multiplication. The first thing you have to do is flip one of the fractions around* and change the division sign to a multiplications sign. Then, you just have to regularly multiply like you would if they were normal fractions.

*Numerator to denominator, denominator to numerator.

Page 13: How to Multiply and Divide Fractions

STEP 1 EXAMPLE

4/6 ÷ 7/8 = 4/6 ÷ 8/7 x 4/6 x 8/7

Page 14: How to Multiply and Divide Fractions

STEP 2 EXAMPLE

4/6 x 8/7

4x8=326x7=42

Page 15: How to Multiply and Divide Fractions

STEP 3 EXAMPLE

Put it in SIMPLEST FORM like you did with multiplication. Make sure you check!

A: 16/21

Page 16: How to Multiply and Divide Fractions

CHECK

Do you understand the concept of multiplying and dividing fractions now? Good. Check if you know with these problems.

5/6 x 7/9

2/5 ÷ 3/5

Page 17: How to Multiply and Divide Fractions

MULTIPLICATION ANSWER

The answer is 35/54.

Here is how.

5 x 7 = 356 x 9 = 54

Page 18: How to Multiply and Divide Fractions

DIVISION ANSWER

The answer is 2/3.

Here is how I got it.

2/5 ÷ 3/5 = 2/5 x 5/3

2 x 5 = 105 x 3 = 15

Page 19: How to Multiply and Divide Fractions

FINAL REVIEW

Last question: What is the fraction of the questions that you got correct divided by the amount you got wrong?

Page 20: How to Multiply and Divide Fractions

ANSWER

There are different answers depending on the amount you got right and wrong. The possibilities are :

• 0 ( 4/0 )• 1 ( 2/2 )

Page 21: How to Multiply and Divide Fractions

THANK YOU FOR PARTICIPATING!!!

Presentation by Frank Wang

PowerPoint by Frank Wang

Examples by Frank Wang

Everything else ( except the methods) by Frank Wang