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Home  >>  CBSE XI  >>  Math  >>  Permutations and Combinations
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Given 5 flags of different colours,how many different signals can be generated if each signal requires the use of 2 flags,one below the other?

$\begin{array}{1 1}(A)\;15\\(B)\;17\\(C)\;20\\(D)\;25\end{array} $

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First place can be filled up in 5 ways.After filling first place,we are left with 4 flags.
$\therefore$ The second place can be filled up in 4 ways.
The total number of signals which can be generated =$5\times 4=20$
Hence (C) is the correct answer.
answered May 13, 2014 by sreemathi.v

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