combinations
nCr
you have n items and how many ways are there to chose r of them
nCr=\(\frac{n!}{r!(n-r)!}\)
remember than n! means n times all numbers before like
3!=321, 5!=54321
9 stations, how many ways are there to chose 6 of them
9C6=\(\frac{9!}{6!(9-6)!}\)=
\(\frac{9!}{6!(3)!}\)=
\(\frac{9*8*7}{3!}\)=
\(\frac{9*8*7}{3*2*1}\)=
\(\frac{3*4*7}{1}\)=
84
84 ways
