​Remember: fractions that share the same denominator have common denominators!

We must have common denominators in order to add or subtract fractions!

​Finding Common Denominators

​Example 1:

​To find common denominators we can...
1. Find the LCM of the denominators.
OR
2. Multiply the denominators and use the answer we get as our common denominator.

​Finding Common Denominators

​Step 1: Find the LCM to get common denominators. The LCM is 10.
Step 2: We must also change the numerator. (Think of equivalent fractions) "Whatever you do to the bottom, you do to the top." Multiply 3 x 2 for the first fraction and 3 x 5 for the second fraction.
Step 3: Now we can add the new fractions!

​More Examples

​Daily Challenge #30: Extreme Challenge: (Solve every problem)

​Write the fractions so they have common denominators. Then compare the fractions

​a. 3/5

​7/15

​b. 5/12

​7/10

​Add or Subtract:

​c. Use common denominators to arrange these fractions in order from least to greatest: 1/2, 3/10, 2/5

​d. 3/4 + 5/6 + 3/8

​e. 7 5/6 - 2 1/2

​f. 4 3/4 + 5 5/8

​g. 4 1/6 - 2 5/9

​h. Write any 2 fractions that do not have the same denominators. Then solve by adding or subtracting.

​Bonus:
(Hint: prime factorization might help)
i. 25/36 + 5/60
and
j. 3/25 - 2/45

​Rules: You and a partner will work through all of these problems together and get as many right as you can in under 20 minutes!