Permutations And Combinations Question 362

Question: Let $ E=(2n+1)(2n+3)(2n+5)…(4n-3)(4n-1); $ $ n>1 $ then $ 2^{n}E $ divisible by

Options:

A) $ ^{n}{C _{n/2}} $

B) $ ^{2n}C _{n} $

C) $ ^{3n}C _{n} $

D) $ ^{4n}C _{2n} $

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Answer:

Correct Answer: D

Solution:

  • [d] Here, $ E=(2n+1)(2n+3)(2n+5)…(4n-3)(4n-1) $ Or $ (2n+1).(2n+2).(2n+3).(2n+4) $ Or $ E=\frac{…………..(4n-1)(4n)}{(2n+2)(2n+4)…(4n)}.\frac{(2n)!}{(2n)!} $ $ E=\frac{(4n)!\cdot n!}{(2n)!2^{n}\cdot (2n)!} $

$ \Rightarrow 2^{n}E=\frac{(4n)!}{(2n)!(2n)!}.n!{{=}^{4n}}C _{2n}.n! $

$ \Rightarrow 2^{n}E $ is divisible by $ ^{4n}C _{2n}. $