Topic 10

What you know and what you are going to know

• You know how to add and subtract whole numbers, like 6 + 9

• Today you are going to learn how to add and subtract fractions with like denominators.

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• How do you How do you add fractions?add fractions?

• How do you How do you subtract subtract fractions?fractions?

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ObjectiveObjective• Add and subtract fractions Add and subtract fractions

and mixed numbers and mixed numbers expressing answers in expressing answers in simplest form.simplest form.

When do you think you might need to add or subtract fractions?

•Following a recipe

Measuring or cutting lengths

Think back to some of the things you already know

• Simplest form

• Equivalent fractions

• Common denominators

• Factors (GCF) and (LCF)

• Multiples (GCM) and (LCM)

• How to compare

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Writing Fractions in Simplest FormWriting Fractions in Simplest Form

• A fraction is in A fraction is in simplest form when simplest form when the only common the only common factor of the factor of the numerator and numerator and denominator is 1. denominator is 1.

1.1. 22 •• 11 = = 22

3 3 •• 1 = 3 1 = 3

2. 2. 2727

3636

1. List the common factors.

2. Find the GCF.

3. Divide by the GCF.

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Mixed Number / Improper FractionMixed Number / Improper Fraction

• When changing a mixed number to an When changing a mixed number to an improper fraction, you need to multiply the improper fraction, you need to multiply the denominator by the integer, then add the denominator by the integer, then add the numerator to the product.numerator to the product.

• Rewrite 4 1/2 as an improper fraction.Rewrite 4 1/2 as an improper fraction.

99//22

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Adding FractionsAdding Fractions

1.1. CheckCheck for common denominators. for common denominators.

2.2. OnceOnce the denominators are the the denominators are the same, add the numerators.same, add the numerators.

3.3. AlwaysAlways simplify your answer. simplify your answer.

4.4. IfIf your answer doesn’t match an your answer doesn’t match an answer choice, try to simplify the answer choice, try to simplify the answer choices.answer choices.

practice

Video with like denominators

• http://www.youtube.com/watch?v=52ZlXsFJULI

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Find the SumFind the Sum

1.1. 8/9 + 2/9 =8/9 + 2/9 =

2.2. 9/16 + 4/32 =9/16 + 4/32 =

3.3. 8 2/3 + 6 1/2 =8 2/3 + 6 1/2 =

• 10/9 = 1 1/910/9 = 1 1/9

• 22/32 = 11/1622/32 = 11/16

• 14 7/6 = 15 1/614 7/6 = 15 1/6

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Subtracting FractionsSubtracting Fractions

1.1. CheckCheck for common denominators. for common denominators.

2.2. OnceOnce the denominators are the the denominators are the same, subtract the numerator.same, subtract the numerator.

3.3. AlwaysAlways simplify your answer. simplify your answer.

4.4. IfIf your answer doesn’t match an your answer doesn’t match an answer choice, try to simplify the answer choice, try to simplify the answer choices.answer choices.

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Find the DifferenceFind the Difference

1.1. 4/5 - 2/5 =4/5 - 2/5 =

2.2. 8/12 - 4/9 =8/12 - 4/9 =

3.3. 9 - 6 5/8 =9 - 6 5/8 =

• 2/52/5

• 8/36 = 2/98/36 = 2/9

• 2 3/82 3/8

video with unlike denominators

• http://www.graspr.com/videos/Adding-and-Subtracting-Fractions-With-UNLIKE-Denominators-1

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Review!Review!

• How do you add fractions?How do you add fractions?

• How do you subtract fractions?How do you subtract fractions?

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Find the Difference, Find the SumFind the Difference, Find the Sum

1.1. 5 - 2 3/45 - 2 3/4

2.2. 4/5 + 3/104/5 + 3/10

• 2 ¼2 ¼

• 1 1 11//1010