generating random number based on points and chance in excel

i have a excel file to choose a winner between my customers download excel file but in 99 percent winners are top 2 customers with maximum points can i make more chances for others with less point?

what i need is : 60 percent chances for top 5 percent of customers/ 20 percent chances for next 20 percent of customers/ 20 percent chances for next 75 percent of customers/ thanx