A combination of a set of distinct object is an unordered arrangement of these objects.

For a set of \(n\) items, thre is only one possible combination.

## k-combinations

To choose \(k\) elements from a wider group on \(n\) an *k-combination* may be used.

For two integers \(n, k\) where \(0 \leq k \leq n\) possible combinations are:
\[
C(n,k) = \frac{n!}{r!(n-k)!}
\]