[tex]\bf _nP_r=\cfrac{n!}{(n-r)!}\qquad \qquad \qquad _9P_5=\cfrac{9!}{(9-5)!}[/tex]
check your calculator for the [!] factorial button.
also bear in mind that most calculators also have an [ₙPᵣ] button, to get Permuations, and you can just use that.
