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Objective Students add and subtract fractions and mixed numbers

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3

• Fill in planner• Today’s Assignment (Practice 5-3)

• Bell Work• Compare the fractions using <,>, or =

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1

3

2

10

9

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6

3

10

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Adding Fractions with common denominators

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4

8

3

8

7

Just add the numerators!

Adding Fractions with different denominators

Problem:

You can’t add fractions with different denominators.

Solution: Turn fractions into equivalent fractions with a

common denominator, preferably the LCD!

Finding the Lowest Common Denominator

• The lowest common multiple of two numbers is the lowest number in BOTH lists of multiples

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1

2

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Multiples of 2 are 2, 4, 6, 8, 10……

Multiples of 3 are 3, 6, 9, 12, ………

What is the lowest common multiple?

Example 1

Finding the Lowest Common Denominator

• The lowest common multiple of two numbers is the lowest number they will BOTH divide into

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1

2

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2 divides into 2, 4, 6, 8…..3 divides into 3, 6, 9….

What is the lowest number 2 and 3 both divide into?

+The Lowest Common Multiple of 2 and 3 is 6 so turn all fractions into sixths

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3

3

3

2

1

You can’t add fractions with different denominators

Special form of 1

3

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2

1

6

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2

2

3

1

6

5

6

2

6

3

10

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10

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10

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2

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1

Lowest common denominator is 10 so make all fractions tenths

Example 2

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3

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Turn both fractions into twelfths

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12

3

12

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Example 3:

Variable Expressions

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1 x

Example 4

46

45

38

31

x

24

203 x

Variable Expressions

mm 3

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3

2

Example 5

m3

42

m3

2

Variable Expressions

52

yy

Example 6

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2

52

5

yy

10

7y10

2

10

5 yy

Adding Mixed Numbers

Find the sum.1

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+ 31

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1. Rewrite the fraction using LCD if denominators are different.

2. Add or subtract the fractions,

then the whole numbers.3. Simplify if possible.

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9 In this problem, the denominators are the same, so begin with step 2.

Let’s Do More Examples!

14

9

31

3+ =9

3

X 3

X 3

47

9

47

8

51

4+ =8

2

X 2

X 2

99

8

= 11

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10

1

8Add the whole numbers.

Example 8 Example 9