Transcript How to Multiply and Divide Fractions

HOW TO MULTIPLY AND DIVIDE
FRACTIONS
By Frank Wang
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.
PART ONE:
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.
HOW TO
This is very easy. There are only two steps to
multiplying fractions. First, Multiply the
numerators together and multiply the
denominators together.
STEP 1 EXAMPLE
4/6
x
7/8
=
?
4x7= 28
6x8= 48
ANSWER: 28/48
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, 14
48: 6, 8, 48, 1, 2, 24, 4, 12, 16, 3
*If 1 is the GCF, it is already in simplest form!
GCF
After that, divide the numerator and the
denominator by the GCF.
28 ÷ 4 = 7
48 ÷ 4 = 12
So, the answer is 7/12.
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: 7,2,1,14
24: 6, 4, 8, 3, 12, 2, 24, 1
14 ÷ 2 = 7
24 ÷ 2 = 12
So, the answer is 7/12.
PART 2:
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.
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.
STEP 1 EXAMPLE
4/6 ÷ 7/8
=
4/6 ÷ 8/7
x
4/6 x 8/7
STEP 2 EXAMPLE
4/6 x 8/7
4x8=32
6x7=42
STEP 3 EXAMPLE
Put it in SIMPLEST FORM like you did with
multiplication. Make sure you check!
A: 16/21
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
MULTIPLICATION ANSWER
The answer is 35/54.
Here is how.
5 x 7 = 35
6 x 9 = 54
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 = 10
5 x 3 = 15
FINAL REVIEW
Last question: What is the fraction of the questions
that you got correct divided by the amount you
got wrong?
ANSWER
There are different answers depending on the
amount you got right and wrong. The possibilities
are :
•
•
0 ( 4/0 )
1 ( 2/2 )
THANK YOU FOR PARTICIPATING!!!
Presentation by Frank Wang
PowerPoint by Frank Wang
Examples by Frank Wang
Everything else ( except the methods) by Frank Wang