Question 473212
Since order matters, you can either compute <font size=1>45</font> <font size=6>P</font> <font size=1>4</font> or you can realize that there are 45 choices for the first slot, 44 for the second, and so on and then multiply those choices to get: 


45*44*43*42 = 3575880



So there are 3575880 different selections possible.