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Home  >>  CBSE XI  >>  Math  >>  Permutations and Combinations
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There are $10$ lamps in a hall.Each one of them can be switched on independently.Find the number of ways in which the hall can be illuminated.

$\begin{array}{1 1}(A)\;10^2\\(B)\;1023\\(C)\;26{10}\\(D)\;10!\end{array} $

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Given :
Total number of lamps =10
Since at least one lamp is to be kept switched on
The total number of ways are
$\Rightarrow 2^{10}-1$
$\Rightarrow 1024-1$
$\Rightarrow 1023$
Hence (B) is the correct answer.
answered May 15, 2014 by sreemathi.v

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