combination

In mathematics, a selection of a number of objects from some larger number of objects when no account is taken of order within any one arrangement. For example, 123, 213, and 312 are regarded as the same combination of three digits from 1234. Combinatorial analysis is used in the study of probability.

The number of ways of selecting r objects from a group of n is given by the formula:

n!/[r!(n − r)!] (see factorial). This is usually denoted by nCr.