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
1/3 + 3/9
*Write your answer in simplest form.
6/9 then simplify to 2/3
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?
List the multiples of the two denominators in order to find the LCD.
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
What do we call fractions that represent the same value, but have different numerators and denominators?
Equivalent Fractions
List the factors of 21
1, 3, 7, 21
4/9 + 1/6 =
*write your answer in simplest form
6/7 - 1/2 =
5/14
9/10 and 5/6
LCD: 30
What are unlike fractions?
Fractions with different denominators.
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
Do you have to find the least common denominator to add or subtract unlike fractions?
No, you need a like denominator, but it doesn't have to be the LEAST common denominator.
List the factors of 8
1, 2, 4, 8