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Home  >>  CBSE XI  >>  Math  >>  Permutations and Combinations
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The number of 5-digit telephone numbers having one of their digits repeated is

$\begin{array}{1 1}(A)\;90,000\\(B)\;10,000\\(C)\;30,240\\(D)\;69760\end{array} $

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1 Answer

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Total number $N=10^5$
Total number without repeated digits =$N_1=10\times 9\times 8\times 7\times 6$
Total no with repeated digits =$N-N_1$
$\Rightarrow 10^5-10\times 9\times 8\times 7\times 6$
$\Rightarrow 69760$
Hence (D) is the correct answer.
answered May 16, 2014 by sreemathi.v
 

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