Remark
Many calculators have a key that will do this in one step. Mine is one of them. So let's start with the answer and then we'll do it the long way.
9C3 = 84. You put it into your calculator as 9 2nF nCr 3 =
Solution
[tex]\dfrac{9!}{(n - 3)!3!} = \dfrac{9*8*7*6!}{6!*3!}=\dfrac{9*8*7}{6}[/tex]
3*4*7 = 84 which is what you set out to show.
