==========================================================
Explanation:
We have five slots which we can label A,B,C,D,E
We start at 8 and count down by 1 each time until all slots are accounted for. Then multiply out those items: 8*7*6*5*4 = 6720
--------------
Another approach is to use the nPr permutation formula.
Plug in n = 8 and r = 5.
[tex]n P r = \frac{n!}{ (n-r)! }\\\\8 P 5 = \frac{8!}{ (8-5)! }\\\\8 P 5 = \frac{8!}{ 3! }\\\\8 P 5 = \frac{8*7*6*5*4*3!}{ 3! }\\\\8 P 5 = 8*7*6*5*4\\\\8 P 5 = 6720\\\\[/tex]
In the second to last line, the "3!" factorial terms cancel out.
We have the string 8*7*6*5*4 show up again to help reinforce the previous section.
