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.CLICK HERE

We need a common denominator to add these fractions.

We need a common denominator to add these fractions. Use Prime factorization to find the Least Common Denominator (LCD)/ Least Common Multiple (LCM)

27 2*1*7*1=14 14 Is the Least Common Denominator (LCD)/Least Common Multiple (LCM)

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

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

x 2 X 7 x = 13 13

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

x 7 X 5 x = 22 22

We need a common denominator to add these fractions. 7, 14, 21, 28, 35, 42, 49, 56, 63 8, 16, 24, 32, 40, 48, 56, 64, 72

x 7 x = 53 53

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

X 3 x 5 x = 19 19

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

x 11 X 3 x = 37 37

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

x 1 X 2 x = 5 5

We need a common denominator to add these fractions. 11, 22, 33, 44, 55, 66, 77… 6, 12, 18, 24, 30, 36, 42, 48, 54, 60, 66, 72

x 11 X 6 x = 29

We need a common denominator to add these fractions.

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

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

x 5 x = = 71

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

x 3 x =

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

x 5 x =

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

x 1 x – 3 = 2 5 3

Try These A F E B C D

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 A F E B C D

To change a mixed number into an improper fraction get MAD…Multiply – Add – Put over Denominator 4 ½ 4 x 2 = = To change an improper fraction into a mixed number divide the numerator by the denominator; whatever is left over is the new numerator…keep the same denominator. For Example: divided 4 equals 2; there is 3 left over

Change the following into Improper Fractions. 1.3 ½ 2.5 5/ / ¾ Change the following into Mixed Numbers / /9 3. 4/3 4. 9/2

Change the following into Improper Fractions ½ = 7/ /8 = 45/ /3 = 37/ ¾ = 63/4 Change the following into Mixed Numbers. 1.40/13 = 3 1/ /9 = 11 1/9 3.4/3 = 1 1/3 4. 9/2 = 4 ½

6 ½ 5 1/ /6 2/6 You MUST have a common denominator to add fractions! Find the least common multiple of 3 and 2. This number is 6. Add the whole numbers Once you have the common denominator, add the fractions, 11 5/6

1.3 1/ ½ + 4 ¼ + 1 ¾ 3.5 1/6 4. 1/ /3 1/4 + 1/2

1.3 1/ ½ + 4 ¼ + 1 ¾ 7 9/20 3 5/4 = 4 1/ /6 4. 1/ /3 1/4 7 5/6 + 1/2 13/12 = 1 1/12

======== To subtract fractions you must have a common denominator! Find the least common multiple for 3 and 6. (In this case, 6) Then multiply! 1616 This is your answer! 6 th Grade HomePage

1.½ 2. 3 ¾ - ¼ - 1 ½ 3.4 1/ /2

1.½ 2. 3 ¾ - ¼ - 1 ½ ¼ 2 ¼ 3.4 1/ /2 2 7/10