+ Fractions: Addition & Subtraction Algebra Seminar 2012-2013.

+

Fractions: Addition & Subtraction Algebra Seminar 2012-2013

Two Fractions can be combined easily when they have a common denominator.

8

7

8

5+

12

43

12

55 +

5

10+

410

13

8+ 4

28

+

Def. Common Denominator- A number that all of the denominators divide into evenly.

+Common Denominator (similar to LCM)

A number all original denominators divide into evenly

12 is a common denominator because 3 and 4 both divide 12 evenly.

3

2

4

3

Least Common Denominator (same as LCM)

To find the least common denominator

* Write the times table list for each denominator

* The smallest number that is in all rows is the least common denominator

+Least Common Denominator

To find the least common denominator• Write the times table list for each denominator• The smallest number that is in all rows is the

least common denominator

+The least common denominator is: 24!!!

so5

6+

34

+78

=2024

+1524

+2124

=5624

=72

=312

+Practice - Find the common denominator for these fractions.

2/3 + 3/5

¾ + 7/12

2/5 + 3/8 + 7/10

What if the denominators do NOT match? If the denominators do not match, you must

find the LCM to change them.

12

51

12

17

12

8

12

93

2

4

3

=

=+

=+5

8+

13

=

1524

+824

=2324

+

Subtracting Fractions

+Subtraction – the process is the same but you will subtract the numerators instead of adding them.

Squirt reminds you to:

1) Get a Common Denominator

2) Subtract

7

8−

34

=

78

−68

=18

+Extra Practice

7

8−

14

=

5

6−

35

= 14

15−

39

=

7

10−

25

=

+Subtraction

What is different about this problem? We have a mixed number!

Lets change them to improper

fractions!

42

5−2

35

=

22

5−

135

=9

5=1

45

Subtraction Practice

73

4−2

56

=

16

10−

46

=

32

4−1

35

=