Permutation vs. Combination

- permutation: nPr = number of arrangements of "r" items taken from a set of "n" distinct items (order matters!!) = $\frac{{n!}}{{\left( {n - r} \right)!}}$

- combination: nCr = number of selections of "r" items taken from a set of "n" distinct items (order does NOT matter!!) = $\frac{{n!}}{{\left( {n - r} \right)!\;\;r!}}$