Question

how do i find the lcd for large denominators like19/70-19/110.

Answer 1

look at the prime factors of 70 and 110:
70 = 2*5*7
110 = 2*5*11
to get the LCD, take the factors they don't have in common 7 and 11 and multiply that with what they have in common, 2*5. So your answer should be (2*5)*7*11=770.

Answer 2

sorry, not your answer but the lcd to the problem...

Answer 3

Write the prime factors in exponential form. Select the largest power of every DIFFERENT factor. That will be your LCM