1. Adding and Subtracting Fractions

2. How to Add or Subtract Fractions
the numerators
2) Keep the same
denominator
3/6 + 2/6 = 5/6

3. Different Denominators
What if the denominator is not the same?

4. What To Do:
Make the denominators the same by finding the least common denominator.
LCD =12
Least Common Denominator (LCD): the smallest number that both denominators can be divided into.

5. Quick Review: Equivalent Fractions
Find an equivalent fraction by dividing the numerator and denominator:
Find an equivalent fraction by multiplying the numerator and denominator:
Find an equivalent fraction by simplifying:
10/15 = 2/3
(Divide by 5)
6/8 = 18/24
(Multiply by 3)
12/16 = 3/4

6. Least Common Denominator (LCD)
9/ /12
= 11/12
Change the fractions to equivalent fractions that have the same denominator.
Fractions must have a common denominator in order to be added or subtracted.
Try to change the fractions so they have the least (or smallest) common denominator, because it makes the calculations easier!

7. A Method for Finding the LCD
Multiples of 6: 6, 12, 18, 24, 30…
Multiples of 4: 4, 8, 12, 16, 20 …
LCD = 12

8. 3/6 + 3/8 = Example 1 12/24 + 9/24 = 3/6 + 3/8 = = 21/24 LCD = 24
3/ /8 =
12/ /24 =
= 21/24
3/6 + 3/8 =
Multiples of 8: 8, 16, 24, 32, 40 …
Multiples of 6: 6, 12, 18, 24 …
LCD = 24

9. Example 2 10/20 - 1/4 = 10/20 – 1/4 = 10/20 - 5/20 = = 5/20 LCD = 20
10/ /20 =
= 5/20
10/20 – 1/4 =
Multiples of 20: 20, 40, 60, 80, 100 …
Multiples of 4: 4, 8, 12, 16, 20 …
LCD = 20

10. Work as a class to race against time!
Race the Clock!
Work as a class to race against time!