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Adding & Subtracting Fractions Teacher Notes: Use this presentation to teach the steps for adding and subtracting fractions with unlike denominators. It is assumed that students have a thorough understanding of the process for making equivalent fractions. CLICK HERE to view a demonstration with opportunities for students to practice making equivalent fractions.

We need a common denominator to add these fractions. +

+ We need a common denominator to add these fractions. Count by 2's 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 Count by 7's 7, 14, 21, 28, 35…

Count by 2's 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 Count by 7's 7, 14, 21, 28, 35… The first number IN COMMON that appears on both lists becomes the common denominator

7 6 13 = = + 7 + 6 = 13 x 7 X 7 x 2 x 2 Make equivalent fractions. Add the numerators = + 7 + 6 = 13 x 2 13

+ We need a common denominator to add these fractions. Count by 7's 7, 14, 21, 28, 35, 42, 49, 56, 63 Count by 5's 5, 10, 15, 20, 25, 30, 35, 40, 45

15 7 22 = + = 15 + 7 = 22 x 5 X 5 x 7 x 7 Make equivalent fractions. Add the numerators = x 7 15 + 7 = 22 22

+ We need a common denominator to add these fractions. Count by 3's 3, 6, 9, 12, 15, 18, 21, 24, 27 Count by 5's 5, 10, 15, 20, 25, 30, 35, 40, 45

x 3 9 Add the numerators = X 3 9 + 10 = 19 x 5 10 + = x 5 19

WAIT!!!! The numerator in the fraction is BIGGER than the denominator! We have to fix that.

How to deal with improper fractions When your numerator is BIGGER than your denominator, you need to convert the improper fraction to a mixed number. To express an improper fraction as a mixed number, divide the denominator into the numerator.

1 = -15 4

+ We need a common denominator to add these fractions. Count by 3's 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33 Count by 11's 11, 22, 33, 44, 55, 66, 77…

15 22 37 = + = 15 + 22 = 37 x 3 X 3 x 11 x 11 Make equivalent fractions. = X 3 x 11 Add the numerators 22 + = 15 + 22 = 37 x 11 37

Improper Fraction ALERT! Don’t forget to divide your numerator by your denominator! is improper. So divide 37 by 33. Your final answer is 1

Now, let’s carry on…

+ We need a common denominator to add these fractions. Count by 3's 3, 6, 9, 12, 15, 18, 21, 24, 27 Count by 6's 6, 12, 18, 24,…

4 1 5 4 + 1 = 5 = + = x 2 X 2 x 1 x 1 Make equivalent fractions. Add the numerators = x 1 4 + 1 = 5 5

We need a common denominator to add these fractions. +

+ We need a common denominator to add these fractions. Count by 5's 5, 10, 15, 20, 25, 30, 35, 40, 45 Count by 9's 9, 18, 27, 36, 45, 54, 63, 72, 81

Count by 5's 5, 10, 15, 20, 25, 30, 35, 40, 45 Count by 9's 9, 18, 27, 36, 45, 54, 63, 72, 81 The first number IN COMMON that appears on both lists becomes the common denominator

36 35 71 = + = x 9 x9 x 5 36 + 35 = 71 x 5 Make equivalent fractions. Add the numerators. + = 36 + 35 = 71 x 5 71

+ We need a common denominator to add these fractions. Count by 12's 12, 24, 36, 48, 60, 72, 84, 96 Count by 8's 8, 16, 24, 32, 40, 48, 56, 64, 72, 79, 80, 88, 96

10 9 19 10 + 9 = 19 = + = x 2 x 2 x 3 x 3 Make equivalent fractions. Add the numerators. + = 10 + 9 = 19 x 3 19

- We need a common denominator to subtract a fraction from another. Count by 5's 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 Count by 11's 11, 22, 33, 44, 55, 66, 77…

Subtract the numerators. 15 x 5 Make equivalent fractions. = x 5 11 x 11 Subtract the numerators. = 15 - 11 = 4 - x 11 4

- We need a common denominator to subtract one fraction from another. Count by 2's 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 … Count by 10's 10, 20, 30…

Subtract the numerators.. 5 x 5 Make equivalent fractions. = x 5 3 x 1 Subtract the numerators.. - = 5 – 3 = 2 x 1 2

Is your fraction SIMPLIFIED? WAIT!!!! Is your fraction SIMPLIFIED?

NOPE! is not simplified. Both 2 and 10 are even, so divide numerator and denominator by 2. Final answer is

Try These A D E B F C

Answers On Next Slide Each click on the next slide reveals an answer. Check your papers. If you discover an incorrect answer, be able to explain your mistake.

Try These 17 27 1 9 A D 1 13 28 13 12 B E 1 19 20 5 21 C F 1