2. A box contains 9 good items and 3 defective items. Each time an item is taken, it is not replaced. What is the probability that 3 defective items have been taken before 2 good items are taken? $\qquad$
$\begin{array}{l}\text { 2. } \frac{1}{55} . \\ P=\frac{3}{12} \times \frac{2}{11} \times \frac{1}{10}+\frac{9}{12} \times \frac{3}{11} \times \frac{2}{10} \times \frac{1}{9}+ \\ \frac{3}{12} \times \frac{9}{11} \times \frac{2}{10} \times \frac{1}{9}+\frac{3}{12} \times \frac{2}{11} \times \frac{9}{10} \times \frac{1}{9} \\ =\frac{1}{55} .\end{array}$