On her vacations Veena visits four cities $(A,\,B ,\, C$ and $D$ ) in a random order. What is the probability that she visits $A$ first and $B$ last ?
On her vacations Veena visits four cities $(A,\,B ,\, C$ and $D$ ) in a random order. What is the probability that she visits $A$ first and $B$ last ?
$S=\left\{\begin{array}{l}A B C D, A B D C, A C B D, A C D B, A D B C, A D C B, \\ B A C D, B A D C, B D A C, B D C A, B C A D, B C D A \\ C A B D, C A D B, C B D A, C B A D, C D A B, C D B A, \\ D A B C, D A C B, D B C A, D B A C, D C A B, D C B A\end{array}\right.$
Let $G$ be the event "she visits $A$ first and $B$ last" $^{\prime \prime}$
$G=\{A C D B, A D C B\}$
So, $n(G)=2$
$P(G)=\frac{n(G)}{n(S)}$ $=\frac{2}{24}=\frac{1}{12}$
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