Permutation and Combination
Permutation
$P(n, ~ r) = \dfrac{n!}{(n - r)!}$
Combination
$C(n, ~ r) = \dfrac{n!}{r! \, (n - r)!}$
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Permutation
$P(n, ~ r) = \dfrac{n!}{(n - r)!}$
Combination
$C(n, ~ r) = \dfrac{n!}{r! \, (n - r)!}$