Ben Brink
Posts:
187
From:
Rosenberg, TX
Registered:
11/11/06
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RE: Permutation problems
Posted:
Aug 12, 2013 2:23 PM
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Dr. Rickert:
I just noticed something else: All posts to this point tacitly assume that "string" implies the adjective "uninterrupted." I see nothing in the original post which explictly excludes a result such as f,r,i,a,s,t,h, (etc.).
Then again, there may be a standard definition of "string" which I've missed. Again, great work on your part, that of Dr. Scales and all others.
Ben
> Date: Mon, 12 Aug 2013 13:35:26 -0400
> From: discussions@mathforum.org
> To: discretemath@mathforum.org
> Subject: Re: Permutation problems
>
> Hi Mark,
>
> > The same fish/rat logic (inclusion/exclusion) needs
> > to be applied to the second problem as well. For
> > example, 9876450123 has been counted three times.
> > I believe the solution is:
> > 7!+8!+7! - (5!+4!+5!) + 2!
>
> Thanks for picking up that double and triple counting.
> I agree with your result.
>
> Peter Scales.
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