Let's say both n = 3 and r = 3.
An example problem could be something like "We have 3 people to pick from and 3 seats to fill".
Each person would get their own seat. The order doesn't matter in a combination, which is why there's only one combination possible. A group like A,B,C is the same as B,C,A.
So in this case, [tex]_3C_3 = 1[/tex] and more generally [tex]_n C_n = 1[/tex] for any positive integer n.
