A permutation of a set of objects is an ordering of the objects in a row. For example, the permutations of the set {1,2,3) are: 123, 132, 213, 231, 312, and 321. An r-permutation of ann element set, denoted P(n,r) is an ordered selection of r elements.
How many permutations are there on n distinct elernents? Justify your answer