Permutation Q: arranging 12 of 20 people in a circle

Hi all,

I've got a short Q about Permutation.

I can see that, for instance, if I'm to determine the number of ways arranging 12 people in a circle, then its: P(11,11)=P(12,12)*1/12=11!

But I can't see, if I'm to determine the ways of arranging 12 people in a circle, by choosing them from 20 people...

thanks for an advance,
Tuugii

\(\displaystyle \L\left( {\begin{array}{c}
{20} \\
{12} \\
\end{array}} \right)\left( {11!} \right).\)

Choose them and then seat them.

many thanks for the very quick reply,

so does that mean: C(20, 12)*P(11,11) right?

Tuugii

Someone please help me by providing the link for a good explanation of Combination? I'm having "trouble" for the last 8days...

thanks for an advance, Tuugii