LCMs/Adding unlike fractions
posted by Alex L. .
Find the least common multiple in each set of numbers.
1) 8,9,12,18
2) 6,8,9,27,36
I have trouble factoring the denominators in this one.
3/7 + 2/5 + 1/10

try a lcd of 70

The LCM is that smallest whole number that each of your given numbers divide into
8 = 2x2x2
9 = 3x3
12 = 2x2x3
18 = 2x3x3
so looking at those, I will need three 2' and two 3's
LCM = 2x2x2x3x3 = 72
As to your second one,
7 = 1x7
5 = 1x5
10 = 2x5
So your lowest common denominator, or the LCM, is
7x5x2 = 70 
I need to rewrite the fractions so that all the denominators are the same.