1996 AIME Problem 13

In triangle A B C, A B=\sqrt{30}, A C=\sqrt{6}, and B C=\sqrt{15}. There is a point D for which \overline{A D} bisects \overline{B C} and \angle A D B is a right angle. The ratio

\frac{\operatorname{Area}(\triangle A D B)}{\operatorname{Area}(\triangle A B C)}

can be written in the form m / n, where m and n are relatively prime positive integers. Find m+n.