Mrs. Brenda Windsor 2008 Adding Fractions with Common Denominators 1.Add the Numerators. 2.Keep the...

Mrs. Brenda Windsor

2008

Adding Fractions with Common Denominators

1. Add the Numerators.

2. Keep the Denominators the same.

3 5+

11 11

=8

11

3 5+

11 11=

+2

9=

9

5

9

16+

4

16=

Reduce or simplify if necessary…

2

15+

3

15=

5

15

5

15÷

5

5=

1

3

What does it mean to reduce

or simplify?

+2

9=

9

4

+3

12=

12

6

+2

15=

15

7

+1

16=

16

1

Adding Fractions with Unlike Denominators

1. Find a common denominator using LCM.

2. Multiply numerator and denominator by LCM.

3. Add the converted fractions.

What is an LCM?

+2

3

=

6

5

We need to create fractions with like denominators in order to add these fractions. This is where we need LCM (Least Common Multiples)

3: 3, 6, 9, 12, 15, 18

6: 6, 12, 18

•The first common multiple is the Least Common Multiple

• This will become the new denominators in order to create like denominators to add fractions.

•List the multiples for each of the factors (denominators)

Adding Fractions with Unlike Denominators

3

7+

3

4=

Multiples of 7:

Multiples of 4:

7, 14, 21, 28

4, 8, 12, 16, 20, 24, 28

3

7

1228

=

3

4 =

21

28

X 4

X 4

X 7

X 7

3 3

7 4 +

12 21

28 28 +

START

READY TO ADD

Common Multiples for these numbers:

6:

12: What is the LCM?


8:



9:



4:



3:

5: What is the LCM?


7:



6:

5: What is the LCM?

+2

3=

9

4

What is the LCM that you need for a common denominator?

+4

9=

12

5


+4

7=

9

5


+2

3=

6

5


+4

9=

2

1


REVIEW

• In order to add fractions, what must you have?

• Explain a simplified fraction

• What is an LCM?

• What are LCMs used for?

• Why is it important to be able to find an LCM?

Mrs. Brenda Windsor 2008 Adding Fractions with Common Denominators 1.Add the Numerators. 2.Keep the...

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