If a set contains elements, then the total number of possible subsets of is .
There are ! different ways of placing items in order.
The number of possible permutations of items taken from a set of items, where , is given by
The number of permutations of items, of which are identical is given by
The number of permutations of items, of which are identical, are identical, and so on, is given by
The number of possible combinations of items (in any order) taken from a set of items, where , is given by