When we add or subtract fractions, we must have common denominators.
There are two ways to find common denominators:
1. Make the larger denominator (smaller pieces) your "goal." Ask, "How can I change my denominator to make it match my goal denominator?"
The circled denominator is my goal. What can I multiply by 5 to get ten? 5 x 2 equals 10. I will do 2 x 2 on the top to make an equivalent fraction.
Now I can add them together (my denominators match!!)
2. Multiply the denominators by each other.
Since three cannot be multiplied by anything to equal 5, we will have to do 3 x 5 and 5 x 3 to make a common denominator of 15. We will have to repeat this process on the top of the fractions (1 x 5) and (2x3) since fractions must be fair!
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