Adding and Subtracting Fractions

1
Adding and Subtracting Fractions

• Number Sense 1.2

2

• How to add/subtract fractions.

• In order to add/subtract fractions, the
  denominator must be the same.
• Example
• ¼ 2/4 ¾
• If the denominator is not the same, you must find
  the least common multiple of the denominators
  (This can also be called the Least Common
  Denominator).

3

• Unlike Denominators
• Step 1
• Use the upside down cake method to determine the
  LCM
• Step 2 The LCM becomes the new denominator for
  each fraction.

• 3/8 1/6
• 8 6
• 4 3
• 2 ? 4 ? 3
• LCM 24

2
4

• Step 3
• Determine what factor multiplies to make the LCM.
  Multiply the numerator by that factor.
• Step 4 Always simplify when possible

5

• 2/3 1/5

• Four Square Method
• Write the steps in you own words.
• 1)
• 2)
• 3)
• 4)

1 5
2 10
3 15
2
Denominator
3
Answer 13/15
6
Practice

• Add.

• Answers

• 1.) 2/3 1/5
• 2.) 4/9 1/3
• 3.) 3/7 1/3
• 4.) 1/2 3/8
• 5.) 3/8 1/4

• 1.) 13/15
• 2.) 7/9
• 3.) 16/21
• 4.) 7/8
• 5.) 5/8