The fractions $\frac{1}{9}, \frac{1}{4}$ and $\frac{1}{18}$ are to be added. What is their lowest common denominator?
(A) 648
(B) 162
(C) 72
(D) 36
(E) 18
The lowest common denominator of three fractions is the least common multiple of the three denominators. The least common multiple of 9,4 and 18 is 36 .

Answer: (D)