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Home  >>  CBSE XI  >>  Math  >>  Permutations and Combinations
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A bag contains 5 black and 6 red balls.Determine the number of ways in which 2 black and 3 red balls can be selected

$\begin{array}{1 1}(A)\;100\\(B)\;300\\(C)\;400\\(D)\;200\end{array} $

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  • $C(n,r)=\large\frac{n!}{r!(n-r)!}$
The number of ways in which 2 black balls out of 5 black balls are selected.
$5C_2$
The number of ways in which 3 red balls out of 6 red balls are selected.
$6C_3$
The number of ways in which 2 black and 3 red balls can be selected.
$\Rightarrow 5C_2\times 6C_3$
$\Rightarrow \large\frac{5\times 4}{1\times 2}\times \frac{6\times 5\times 4}{1\times 2\times 3}$
$\Rightarrow 10\times 20$
$\Rightarrow 200$
Hence (D) is the correct answer.
answered May 14, 2014 by sreemathi.v
 

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