Permutations And Combinations Question 244
Question: If $ {}^{n}P_4\ :\ {}^{n}P_5=1:2 $ , then $ n= $ [MP PET 1987; RPET 1996]
Options:
A) 4
B) 5
C) 6
D) 7
 Correct Answer: C $ \frac{n\ !}{(n-4)\ !}\times \frac{(n-5)\ !}{n\ !}=\frac{1}{2}\Rightarrow n-5=2\Rightarrow n=7 $Show Answer
  Answer:
Solution:
 BETA
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