Ans: (a) $\dfrac{68}{609}$ (b) $\dfrac{530}{609}$
- The required probability
$\begin{array}{cl}
= & \dfrac{C^{18}_4}{C^{30}_4} \\
= & \dfrac{68}{609}
\end{array}$ - The required probability
$\begin{array}{cl}
= & 1- \dfrac{C^{18}_4}{C^{30}_4}-\dfrac{C^{12}_4}{C^{30}_4} \\
= & \dfrac{530}{609}
\end{array}$
