Adding Fractions with Unlike Denominators
1/4 + 2/3 =
3/12 + 8/12 = 11/12
4/5 - 1/3 =
12/15 - 5/15 = 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.
5/15 divided by 5/5 = 1/3
True or False:
4/9 + 1/6 = 10/18
False.
8/18 + 3/18 = 11/18
True or False:
4/3 - 2/7 = 1 1/21
True.
28/21 - 6/21 =
22/21 OR 1 1/21
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.
11/12 + 7/15 =
55/60 + 28/60 =
83/60 OR 1 23/60
11/12 - 7/15 =
55/60 - 28/60 =
27/60
reduced form: 9/20
1/6 and 4/21
LCD: 42
Add and subtract 3/4 and 1/5
15/20 and 4/20
Addition = 19/20
Subtraction= 11/20
Simplify: 28 / 35
What is 4/5?
1/2 + 1/3 + 1/4 =
6/12 + 4/12 + 3/12 =
13/12 OR 1 1/12
6/7 - 1/2 - 1/28 =
24/28 - 14/28 - 1/28 = 9/28
9/10, 5/6, and 2/3
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
What is 4/5?
1/4 + 3/7 + 2/3 =
21/84 + 36/84 + 56/84 =
113/84 OR 1 29/84
9/10 - 1/4 - 1/3 =
54/60 - 15/60 - 20/60 = 19/60
11/14, 17/42, and 2/3
LCD: 42
What is the last step in the process of adding and subtracting fractions?
Use the greatest common factor to simplify 42/36
42/36 divided by 6/6 = 7/6 = 6/6+1/6 = 1 1/6
OR
42/36 = 36/36 + 6/46 = 1 6/36 divided by 6/6 = 1 1/6