The Least Common Denominator of 1/9, 1/18, 1/100, 1/30 is as follow:

9 = 3 x 3
18 = 3 x 3 x 2
100 = 5 x 5 x 2 x 2
30 = 2 x 3 x 5

Therefore, the LCD = 3 x 3 x 2 x 5 x 5 x 2 = 900