Do you need a common denominator to add or subtract fractions?
How do you add fractions?
5
7 =
+
2
3
How do you subtract fractions?
5
7
=
3
2
Example 1
A]
B]
C]
Find the Least Common Denominator (LCD)
,
,
Find the Least Common Denominator of these three fractions.
Example 2
A]
B]
C]
Adding/Subtracting with like denominators
A]
3x2 x ­ 2
+
3x ­ 2
3x ­ 2
B]
3x2 ­
3x ­ 2
x ­ 2
3x ­ 2
Example 3
Adding/Subtracting with different denominators
Step 1: Find the least common denominator (LCD)
Step 2: Multiply each fraction, top and bottom, by any factor missing from the LCD.
Step 3: Distribute and add/ subtract the numerators. (Don't forget to distribute the negative if you are subtracting!!)
Step 4: Simplify. (Don't forget to check if anything will factor further!!)
A]
B]