4!=4321=24
11!=1110987654321=39916800
7!=765432*1=5040
n choose k
how many ways are there to choose k rollercoasters from n choices?
\(\left(\begin{array}{ccc}n\\k\end{array}\right)\)=\(\frac{n!}{k!(n-k)!}\)
\(\left(\begin{array}{ccc}11\\4\end{array}\right)\)=\(\frac{11!}{4!(11-4)!}\)=\(\frac{39916800}{24(7)!}\)=\(\frac{39916800}{24(5040)}\)=\(\frac{39916800}{120960}\)=330
330 ways
