** Permutation**:

1: The action of changing the arrangement, especially the linear order, of a set of items.

2: All possible arrangements of a collection of things, where the order is important.

__Example__: You want to visit the homes of three friends Alex ("a"), Betty ("b") and Chandra ("c"), but haven't decided in what order. What choices do you have?

Answer: {a,b,c} {a,c,b} {b,a,c} {b,c,a} {c,a,b} {c,b,a}

__Combination__:

A collection of things, __in which the order does not matter__.

__Example__: If you are making a sandwich, how many different combinations of 2 ingredients could you make with cheese, mayo and turkey?

Answer: {cheese, mayo}, {cheese, turkey} or {mayo, turkey}