Ans: (a) $\dfrac{161}{3876}$ (b) $\dfrac{3715}{3876}$
- The required probability
$\begin{array}{cl}
= & \dfrac{C^7_4 + C^9_4}{C^{19}_4} \\
= & \dfrac{161}{3876}
\end{array}$ - The required probability
$\begin{array}{cl}
= & 1 – \dfrac{161}{3876} \\
= & \dfrac{3715}{3876}
\end{array}$
