perms and combs

Permutations, has several different meanings, but all are related to “the act of permuting”, rearranging objects and values. They occur in almost every domain of mathematics. It is an arrangement of numbers in an order . For example there are six permutations of the set {1,2,3}, namely (1,2,3), (1,3,2), (2,1,3), (2,3,1), (3,1,2), and (3,2,1).

The formula for permutation is:

                                nPr =n!/(n-r)

Combination- is a way of selecting several things out of a large group where the order doesn’t matter. In smaller cases you can count the number of combination. When the set gets larger you have to use difficult mathematics to find the number of combinations.

The combination formula:

              (nk)=n(n-1)…(n-k+1)/k(k-1)…1