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Permutations Formula

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Permutations Formula

by krishna kumar » Mon Feb 21, 2011 9:46 pm
Hi All,

Can someone please help with a formula .

How to find the number of permutations of 7 things taken 3 at a time where 2 are of one type and 5 are of another type.

I know that the formula for finding the permutations of 7 things where 2 are of one type and 5 are of another type is

7!/ (2! * 5!).


Thanks in advance.

krishna kumar
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by Anurag@Gurome » Tue Feb 22, 2011 8:56 pm
krishna kumar wrote:Hi All,

Can someone please help with a formula .

How to find the number of permutations of 7 things taken 3 at a time where 2 are of one type and 5 are of another type.

I know that the formula for finding the permutations of 7 things where 2 are of one type and 5 are of another type is

7!/ (2! * 5!).


Thanks in advance.

krishna kumar
Let's take an example for this: Find the number of permutations of 4 letters from the word ACCELERATOR.

It should be 11P4/(2!)^4, as A, C, E, and R occur two times.

11P4/(2!)^4 = 11!/(7!)(16) = 495
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