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# Add and Subtract Fractions - PowerPoint PPT Presentation

Add and Subtract Fractions. Brigitte Steinmetz Beyond Limits Education. Objectives. To add/subtract fractions that have common denominators. To add/subtract fractions that have uncommon denominators using the least common denominator.

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Presentation Transcript

Brigitte Steinmetz

Beyond Limits Education

• To add/subtract fractions that have common denominators.

• To add/subtract fractions that have uncommon denominators using the least common denominator.

• To estimate sums and differences with fractions using benchmarks.

• To identify what information should be written down in Cornell notes.

• Using your fraction cubes, make the following fractions:

38

58

+

1/8

1/8

1/8

1/8

1/8

1/8

1/8

1/8

38

58

+

88

1/8

=

1/8

1

1/8

1

1

=

1/8

1/8

1/8

1/8

1/8

1/8

• Using your fraction cubes, make the following fraction:

58

38

-

Now subtract 3 eights.

1/8

1/8

1/8

1/8

1/8

58

38

-

28

1/8

=

1/8

=

14

1/8

1

4

1/8

1/8

• Using your fraction cubes, make the following fractions:

12

14

+

+

12

14

14

14

14

14

12

24

12

=

24

14

+

34

• Using your fraction cubes, make the following fraction:

23

12

-

Now subtract 1 half.

16

13

16

-

12

16

13

16

Subtract Unlike Fractions

=

?

16

16

13

16

12

16

13

16

• Using your fraction cubes number line, estimate the sum of:

38

45

+

1/8

4/8

5/8

6/8

7/8

8/8

2/8

3/8

1/2

0

1

1

2

38

close to

• Using your fraction cubes number line, estimate the sum of:

38

45

+

2/5

3/5

1/5

4/5

1/2

0

1

45

close to

1

• Using your fraction cubes number line, estimate the sum of:

38

45

+

1

2

1

2

+

=

1

1

• To add/subtract unlike fractions you need to rename them as like fractions.

• Least Common Denominator – is the least common multiple of two or more denominators.

• Using your fraction cubes, make the following fractions:

23

14

+

16

13

16

16

13

14

16

23

Multiples of 3: 3, 6, 9, 12

Multiples of 4: 4, 8, 12

14

1/12

16

13

1/12

1/12

16

1/12

1/12

1/12

LCD = 12

16

13

1/12

1/12

14

1/12

1/12

1/12

1/12

16

1/12

1/12

1/12

1/12

23

44

812

=

X

14

33

312

=

X

812

312

+

1112

• Using your fraction cubes, make the following fraction:

34

16

-

Now subtract 1 sixth.

14

14

14

16

34

Multiples of 4: 4, 8, 12

Multiples of 6: 6, 12

1/12

16

14

1/12

1/12

1/12

14

1/12

1/12

LCD = 12

1/12

1/12

1/12

16

1/12

14

1/12

1/12

1/12

1/12

1/12

1/12

34

33

912

=

X

16

22

212

=

X

912

212

-

712

• Using your fraction cubes, make the following fractions:

3

8

14

2

+

1

1

1

1

1/8

14

1/8

1/8

3

8

2

Multiples of 4: 4, 8

Multiples of 8: 8

14

1

1

1

1

LCD = 8

1/8

14

1/8

1/8

1/8

1/8

11

3

8

3

8

2

2

=

X

22

2

8

14

1

1

=

X

3

8

2

2

8

1

+

5

8

3

• Using your fraction cubes, make the following fractions:

3

8

14

2

-

1

Now subtract one and one fourth.

1

1

1/8

1/8

1/8

3

8

2

Multiples of 4: 4, 8

Multiples of 8: 8

14

1

1

1

1

LCD = 8

1/8

14

1/8

1/8

1/8

1/8

11

3

8

3

8

2

2

=

X

22

2

8

14

1

1

=

X

3

8

2

1

1

2

8

1

-

1

8

1

1/8

1/8

1/8

3

8

2

2

8

1

-

1

8

1

• Using your fraction cubes, make the following fraction:

3

8

1

2

-

Now subtract one and three eighths.

1

1

• In order to do this you must rename one of the two whole numbers.

8

8

1

2

=

1/8

1

1

1

1/8

1/8

1/8

1/8

1/8

1/8

1/8

• Now go through the same steps as before to…

3

8

1

2

-

8

8

1

1/8

1

1/8

3

8

1

-

1/8

1/8

1/8

5

8

1/8

1/8

1/8