Question

Which number is NOT a common

of the fractions being
denominator
added?
2/9 + 5/12

A 108
(B) 72
(C) 36
(D) 24

Answer 1

Check the picture below.

now, doing a prime factoring on both the denominators, notice, the repeated factors get used only once in the LCD calculation, so the red "3" only goes once in the LCD and then the others, so the LCD for both of those is 3*3*2*2 = 36.

"L" in LCD stands for Least, so that's the smallest, however we can have a CD that's no small and is simply a multiple of the LCD, let's check who isn't an LCD or CD

`\begin{array}{rllll} 108=3\cdot 36 & \bigotimes\\\\ 72=2\cdot 36& \bigotimes\\\\ 36=1\cdot 36&\bigotimes\\\\ 24&\textit{\LARGE \checkmark} \end{array}`