Is there a faster way to add/subtract fractions then having to draw a factor tree each time? Do you really have to draw a factor tree and work with primes every time you encounter adding or subtracting fractions? 
Not this way - LCM(8,15)...
15: 15, 30, 45, 50, 65, *80* --
8: 8, 16, 24, 32, 40, 48, 56, 64, 72, *80* -- 

This makes adding and subtracting fractions quite a lot of work. 
What is the most efficient and effective practice in regards to dealing with adding or subtracting fractions? Is there a faster way to add or subtract fractions? I heard of the "Butterfly Method" but it involves a lot of rules. The factor tree seemed easier. I came here to see if determining the least common denominator of two fractions can be done even more efficiently.

Google or Youtube search: The fast way to adding and subtracting fractions.
https://www.youtube.com/watch?v=lKiR4BBt6TE . Number 3 has like factors. Cancel them out yields your result. 
