Notes by Lex Toumbourou

Unlike Permutation, combinations are unordered set.

An r-combination of elements of a set is an unordered selection of r elements from the set.

The number of r-combinations of a set with n distinct elements is denoted by $C(n, r) = \binom{n}{r}$

The notation used is called binomical coefficient

Number of combinations * The number of r-combinations of a set with n distinct elements can be formulated as: * $C(n, r) = \frac{n!}{(n-r)!r!} = \frac{P(n, r)}{r!}$ * $C(n, r)$ can be referred to as n choose r * It follows that $C(n, r) = C(n, n - r)$