Let the total number of gems be $x$

D = $\frac{2x}{3}$
R = $\frac{x}{3}$

Given: $\frac{D_1}{x} . \frac{D_2}{x-1} = 5/12$

$D_1 = \frac{2x}{3}$
$D_2 = \frac{2x}{3} - 1 = \frac{2x-3}{3}$

Therefore, $\frac{2(2x-3)}{9(x-1)} = \frac{5}{12}$

Solve for $x = 9$

Now, Prob. of selecting two Rubies without replacement = $(\frac{3}{9})(\frac{2}{8}) = \frac{1}{12}$

Hence, option C