答案：(a) $\dfrac{360}{1001}$ (b) $\dfrac{5}{11}$
- 所求的概率
$\begin{array}{cl}
= & \dfrac{C^5_2C^9_2}{C^{14}_4} \\
= & \dfrac{360}{1001}
\end{array}$ - 所求的概率
$\begin{array}{cl}
= & \dfrac{C^5_2C^9_2}{C^{14}_4} + \dfrac{C^5_3C^9_1}{C^{14}_4} + \dfrac{C^5_4}{C^{14}_4} \\
= & \dfrac{5}{11}
\end{array}$
