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Home  >>  CBSE XI  >>  Math  >>  Permutations and Combinations
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Using the digits 1,2,3,4,5,6,7,a number of 4 different digit is formed.Find (a) How many numbers are formed

$\begin{array}{1 1}(A)\;840\\(B)\;125\\(C)\;150\\(D)\;175\end{array} $

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On the first digit =7choice
On the second digit =6choice
On the third digit =5choice
On the fourth digit =4choice
So the total no. of numbers is $7\times 6\times 5\times 4$
$\Rightarrow 840$
Hence (A) is the correct answer.
answered May 19, 2014 by sreemathi.v

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