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Home  >>  CBSE XI  >>  Math  >>  Permutations and Combinations
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Evaluate $\large\frac{n!}{(n-r)!}$ when $n=6,r=2$

$\begin{array}{1 1}(A)\;40\\(B)\;30\\(C)\;50\\(D)\;60\end{array} $

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1 Answer

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  • $n!=n(n-1)(n-2)......(3)(2)(1)$
$\large\frac{n!}{(n-r)!}=\frac{6!}{(6-r)!}$
$\Rightarrow \large\frac{6!}{(6-2)!}$
$\Rightarrow \large\frac{6!}{(4)!}$
$\Rightarrow \large\frac{6\times 5\times 4\times 3\times 2\times 1}{4\times 3\times 2\times 1}$
$\Rightarrow 30$
Hence (B) is the correct answer.
answered May 13, 2014 by sreemathi.v
 
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