A) 6
B) 7
C) 8
D) 9
Correct Answer: C $ \frac{^{n}P_4}{^{n}C_5}=30\Rightarrow \frac{n\ !}{(n-4)\ !}\times \frac{1}{\frac{n\ !}{5\ !(n-5)\ !}}=30 $ $ \Rightarrow (n-4)=4\Rightarrow n=8 $ .
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