# Permutations

** Permutations** examine the number of ways a group of objects can be ordered, if you have n items, you will have n! ways in which they can be ordered.If you have 10 items, and you want to determine how many different ways they can be ordered, you use this principle again. This time, you will have 10 options for the first spot, 9 for the second, and so on, so you will have 10*9*8*7*6*5*4*3*2*1 or we can use the notiation of !, so we have 10!, which is read as “10 factorial”.However, if you only want to select r items in order out of the n items, you will use this permutation formula:

_{n}P

_{r}= n!/(n-r)!

The following video goes over this Permutation Formula and is about 4 minutes.