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Q&A #3398

Teachers' Lounge Discussion: Permutations and counting arrangements

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From: Onder <onder.secen@gmail.com>
To: Teacher2Teacher Public Discussion
Date: 2008030523:22:01
Subject: Re: HELP



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

multiply the first fraction with a and second fraction with n to make
the denominators same.-> a!n!

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

a(a-1)!=a! and n(n-1)!=n! so


a              +          n         a+n
-----------          ----------  = ------
a!n!                    a!n!        a!n!

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