Fractions Review

Fractions

A number in the form

Numerator

Denominator

OrND

Fractions

The denominator can never be equal to 0.

0

12=

Does not exist!

Fractions

A fraction with a numerator of 0 equals 0.

156

0= 0

4

0= 0

Fractions

• If the numerator is larger than the denominator, it is called an improper fraction.

Find the improper fraction

11

7

12

10

73

56

9

4

8

10

Math with Fractions

Four basic functions

• Multiply

• Divide

• Add

• Subtract

Multiplication

• Multiply the numerators and put in the numerator of the result

• Multiply the denominators and put in the denominator of the result

8 9 8 x 9 72

47 7 x 4 28= =x

Multiplication - Let’s Try It!

9 2

17=x

5 3

17=x

7 11

94=x

4 14

730=x

18

7

15

7

77

36

56

210

56

210 These numbers get pretty big!

What if we needed to multiply again?

Let’s make the fraction more simple, so it will be easier to use in the future.

Simplification

• Divide by the Greatest Common Factor

72

28But what is a Common Factor?

Factors

• A factor is a number that can be divided into another number with no remainder

– 8’s factors are:• 1 (8/1 =8)• 2 (8/2 = 4)• 4 (8/4 = 2)• 8 (8/8 = 1)

– 3 is NOT a factor of 8, because 8 is not evenly divisible by 3 (8/3 = 2 with R=3)

Common Factors

• A common factor is a factor that two numbers have in common

– For example, 7 is a factor of both 21 and 105, so it is a common factor of the two.

– The greatest common factor is the largest factor that the two number share

So let’s go back to our simplification problem from before…

Simplification

• Divide both numerator and denominator by the Greatest Common Factor

72

28 Factors are 1, 2, 4, 7, 14, 28

Factors are 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 48, 72

Greatest Common Factor is 4

2872 ÷

÷ 44

==

718

So7228

=7

18

Simplification - Let’s Try It!

3

1

7

2

3

1

63

18=

5

2

114

78=

7

2

19

13

9

3=

84

24=

21

7=

15

6=

Division

• Just like multiplication with one more step• Invert the second fraction and multiply

8 2

13=÷

8 1

23x =

8

6

Division - Let’s Try It!

9 217

=÷

=5 3

17÷

7 1194

=÷

=4 10

720÷

914

5

21

6344

7

50

Addition• To add two fractions, you must make

sure they have a Common Denominator

8

3

16

5+

What is a Common Denominator?

Common Denominator

• A common denominator is a number with which both of the denominators share at least one factor that is not the number 1

– For example, if the denominators are 4 and 7, then a common denominator is 28.

– 28 shares the factors 1, 2 and 4 with the number 4, and the factors 1 and 7 with the number 7.So let’s go back to our simplification problem from before…

Addition• To add two fractions, you must make sure

they have a Common Denominator• What can you multiply each fraction by to give the

smallest common denominator?

83

165+

The smallest number that has both of these as factors is 16

8 goes into 16 two times 16 goes into 16 one time

166

83

22x = 16

5165

11x =

166

165+ =

1611

Once you have a common denominator, add the numerators.

Addition - Let’s Try It!

4 211

=+

=8 3

26+

16 824

=+

=16 4

3 13+

43

12

17

21

16

25

Subtraction• To subtract two fractions, they also must

have a Common Denominator• What can you multiply each fraction by to

give the smallest common denominator?

8

3

16

5-

The smallest number that has both of these as factors is 16

8 goes into 16 two times 16 goes into 16 one time

166

=83

22x

165

=165

11x

166

165- =

161

Once you have a common denominator, subtract the numerators.

Subtraction - Let’s Try It!

=8 2

17-

8 2

16=-

=16 8

39-

4 16

75=-

8

3

4

1

16

3

16

13

Review

• A fraction has a numerator and a denominator

• The denominator can never be 0

• You can multiply, divide, add and subtract fractions

• A common factor is a number that both denominators are evenly divisible by

• A common denominator is a number that both denominators share a factor with