Adding Fractions with Unlike Denominators
1/4 + 2/3 =
11/12
4/5 - 1/3 =
7/15
1/2 and 3/5
LCD: 10
If the denominators are the same for two fractions, do we have to find the least common denominator (LCD)?
No, we can add or subtract the fractions as is.
List the factors of 18
1, 2, 3, 6, 9, 18
4/9 + 1/6 =
*write your answer in simplest form
11/18
4/3 - 2/7 =
22/21
5/12 and 2/9
LCD: 36
What is the first thing you do when you are adding or subtracting fractions with unlike denominators?
Find the least common denominator (LCD) for all of the fractions.
List the factors of 30
1, 2, 3, 5, 6, 10, 15, 30
3/4 + 1/9 =
31/36
3/4 - 1/9 =
23/36
1/7 and 4/8
LCD: 56
Add and subtract 3/4 and 1/5
15/20 and 4/20
Addition = 19/20
Subtraction= 11/20
List the factors of 21
1, 3, 7, 21
1/2 + 1/3 =
5/6
6/7 - 1/2 =
5/14
9/10 and 5/6
LCD: 30
What are 2 ways you can get two fractions with unlike denominators to have the same denominator?
1) Find the least common denominator (LCD)
2) Multiply the two denominators by one another
List the factors of 9
1, 3, 9
1/4 + 3/7 =
19/28
9/10 - 1/4 =
*Write your answer in simplest form
13/20
1/4 and 2/3
LCD: 12
What is the last step in the process of adding and subtracting fractions?
List the factors of 8
1, 2, 4, 8