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If ${ }^n P_5=9 \times{ }^{n-1} P_4$, then the value of $n$ is
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The correct answer is:
$9^{\prime}$
$\frac{{ }^n P_5}{n^{n-1} P_4}=9 \Rightarrow \frac{n!}{(n-5)!} \times \frac{(n-5)!}{(n-1)!}=9 \Rightarrow n=9$
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