Combinations and Permutations

Counting selections (order irrelevant) and arrangements (order matters).

(r n) = \frac{n !}{r ! ( n - r )!}, P (n, r) = \frac{n !}{( n - r )!}

Variables

Each combination of $r$ items can be arranged in $r!$ ways, so $P (n, r) = r! (r n)$ .

$(3 10) = 120$ , $P (10, 3) = 720$ .

Compute combinations (nCr), permutations (nPr) and factorials with formulas and steps.

Binomial Probability

Probability of exactly k successes in n independent trials.