Adding and Subtracting Fractions with Like Denominators

LCD, LCM and how to add and subtract fractions with like denominators

LCM

• Least Common Multiple: can be found by finding the multiples for values and the lowest one in common is the LCM

• EX: 4 4. 8, 12, 16, 20, 24

• 6: 6, 12, 18, 24, 30, 36

• The lowest common multiple is 12

• This can be used to make the denominators in fractions that have 4 and 6 into a common denominator of 12.

• That is where LCD is termed. Least Common denominator.

Multiple Choice

What is the LCM of 7 and 14?

• 14

• 7

• 2

• 28

Multiple Choice

What is the LCM of 4 and 6?

• 12

• 6

• 2

• 24

Multiple Choice

What is the LCM of 6 and 15?

• 15

• 30

• 3

• 10

Multiple Choice

What is the LCM of 15 and 30?

• 5

• 3

• 30

• 15

Multiple Choice

What is the LCM of 2 and 14?

• 28

• 7

• 14

• 2

Multiple Choice

What is the LCM of 5 and 17?

• 85

• 5

• 3

• 75

Multiple Choice

What number could be a common denominator for these two fractions?
1/5   and   5/6?

• 30
• 11
• 6
• 5

Multiple Choice

What number could be a common denominator for these two fractions?
2/3   and   3/4

• 3
• 4
• 7
• 12

Multiple Choice

Fill in the missing multiple.
3:  3, 6, 9, ___, 15, 18, 21

• 10
• 11
• 12
• 13

Multiple Choice

What number could be a common denominator for these two fractions?
1/5   and   5/6?

• 30
• 11
• 6
• 5

Multiple Choice

What number could be a common denominator for these two fractions?
2/3   and   3/4

• 3
• 4
• 7
• 12

Adding and subtracting fractions

• The most important fact when adding and subtracting fractions: The denominators need to be the same.

• That is where the LCD comes into play.

• If the denominators are not the same you need to find the LCM and change the denominators.

• That will be the next lesson. Today we are working with only fractions that have the same denominator.

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Adding and subtracting like fractions

•  $\frac{2}{5}+\frac{1}{5}=\frac{3}{5}$  

• Look at the denominators.  They are the same.  When they are the same only add the numerators.

• Use the same rule when subtracting fractions with the same denominators.

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Multiple Choice

11/16 - 3/16

• 1/2
• 1/4
• 1/8
• 1/16

Multiple Choice

What is ¹⁵/₁₆ - ¹²/₁₆?

• ¹/₃
• ⁴/₁₆ or ¹/₄
• ³/₁₆
• ²/₁₆ or ¹/₈

Multiple Choice

What is ¹/₈ + ⁵/₈?

• 1
• ⁶/₁₆ or ³/₈
• ⁶/₈ or ³/₄
• ²/₄ or ¹/₂

Multiple Choice

Solve and SIMPLIFY:

2/8 + 4/8

• 3/4

• 6/8

• 6/16

• 3/8

Multiple Choice

  How do you add two fractions with like denominators?

• Add the denominators; keep the numerators the same
• Add the numerators and add the denominators
• Add the numerators to the denominators
• Add the numerators and keep the like denominators

Multiple Choice

Simplify the fraction to lowest terms:
4/12

• 2/6
• 1/3
• 1/6
• 1/4

Multiple Choice

4/6 - 1/6 = ?

• 5/6

• 1/12

• 3/6

• 5/12

Multiple Choice

What is the sum of the following equation in lowest terms:
2/12 + 3/12 =

• 1/2
• 5/12
• 6/12
• 5/24

Multiple Choice

• 4/5
• 4/10
• 2/5
• 5