how would you solve for r in this situation:(adsbygoogle = window.adsbygoogle || []).push({});

P(5, r) = 20

Now I understand you cant use trial and error to find that r=2 but is there any other way using an algebraic technique. Itried something like this..

[tex] \frac{5!}{(5-r)!}=20[/tex]

then

[tex]\frac{5\times4\times3\times2\times1}{20}=(5-r)![/tex]

[tex]6=(5-r)![/tex]

now i don't know what to do next

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# Homework Help: How to find r in the equation P(5,r)=20

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