Answer :
[tex]_n C_r = \frac{n!}{r!(n-r)!}[/tex]
[tex]_n C _r[/tex] -- the number of combinations of r objects in total n objects.
So for r=6, n=20 we have
[tex]_n C_r = \frac{20!}{6!(20-6)!} = 38760[/tex]
[tex]_n C _r[/tex] -- the number of combinations of r objects in total n objects.
So for r=6, n=20 we have
[tex]_n C_r = \frac{20!}{6!(20-6)!} = 38760[/tex]