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Q&A #3398

Teachers' Lounge Discussion: Permutations and counting arrangements

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From: Sarah <saw109@hotmail.com>
To: Teacher2Teacher Public Discussion
Date: 2004050609:16:30
Subject: Re: Re: HELP



1                   1              a+n
------     +      -------    =   --------
(a-1)!n!          a!(n-1)!         a!n!


a!(n-1)!  +  (a-1)!n!        a+n
---------------------   =   ------
(a-1)!a!(n-1)!n!             a!n!


a(a-1)!  (n-1)!   +  n(n-1)!   (a-1)!         a+n
-------------------------------------    =   ------ 
      (a-1)!a!(n-1)!n!                        a!n!


(a-1)!(n-1)! [a+n]       a+n
---------------------   = -----
(a-1)!(n-1)!a!n!           a!n!

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