# 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.

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19-Jan-2016

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• Topic 10

• What you know and what you are going to knowYou 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.

• *

How do you subtract fractions?

• *ObjectiveAdd and subtract fractions and mixed numbers expressing answers in 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 knowSimplest formEquivalent fractionsCommon denominatorsFactors (GCF) and (LCF)Multiples (GCM) and (LCM)How to compare

• *Writing Fractions in Simplest FormA fraction is in simplest form when the only common factor of the numerator and denominator is 1.

2 1 = 2 3 1 = 3

2. 27 36

1. List the common factors.2. Find the GCF.3. Divide by the GCF.

• *Mixed Number / Improper FractionWhen changing a mixed number to an improper fraction, you need to multiply the denominator by the integer, then add the numerator to the product.

Rewrite 4 1/2 as an improper fraction.9/2

• practice

• *Find the Sum8/9 + 2/9 =

9/16 + 4/32 =

8 2/3 + 6 1/2 =

10/9 = 1 1/9

22/32 = 11/16

14 7/6 = 15 1/6

• *Find the Difference4/5 - 2/5 =

8/12 - 4/9 =

9 - 6 5/8 =

2/5

8/36 = 2/9

2 3/8

• *Review!How do you add fractions?

How do you subtract fractions?

• *Find the Difference, Find the Sum5 - 2 3/4

4/5 + 3/10

2

1 1/10

BAIP Instructional Support Version 2**Writing Fractions in Simplest Form (PowerPoint #2)Teacher prompt: Introduce the term simplest form to students by telling them that a fraction is in simplest form when the only common factor of the numerator and denominator is 1. Teacher prompt: Ask students to list all of the factors of 2.Student response: The factors of 2 are 1, 2.Teacher prompt: Now list all of the factors of 3.Student response: The factors 3 are 1, 3.Teacher prompt: If I asked you to write the fraction 2/3 in simplest form, you would write 2/3 because the only factor the 2 and the 3 have in common is 1. One is the common factor. When you divide both the 2 and 3 by 1 you will still have the fraction 2/3. This means 2/3 is already written in simplest form.Teacher prompt: Now lets write the fraction 27/36 in simplest form. Working with a partner, list all of the factors of 27. List the factors in order from least to greatest. Student response: 27: 1, 3, 9, 27.Teacher prompt: Good. Now, with your partner, list the factors of 36 in order from least to greatest.Student response: 36: 1, 2, 3, 4, 6, 9, 12, 18, 36Teacher prompt: Using these two lists we are going to find the greatest common factor of 27 and 36.Teacher prompt: Show the two lists on the board, one underneath the other.27: 1, 3, 9, 27 List the factors for the numerator and denominator.36: 1, 2, 3, 4, 6, 9, 12, 18, 36 Find the greatest common factor (GCF)Teacher prompt: 9 is the greatest common factor. Use this number to divide both the numerator and denominator by. Rewrite the fraction in simplest form. Show your work.Student response: 27 9 = 3 36 9 = 4