To be honest, if you are trying to punch well above your weight, the girls are always going to say no. You need to ask girls whom are on a similar rating scale as you..
For example, if you are a 10 in looks and your personality is a 2, then you are on average a 6... so go for a girl whom you see is a 6 in your books. If you are a 4 in the looks department, but are a 10 in personality, then you are average 7... so go for a girl in that range...
I then kind of believe your success rate will be pretty good.
I'm not following your question.. If it's the same girl she can reject you 100, 200, 500 times and she might never say yes. If it's different girls then there's no number to judge it by. Sometimes you just get lucky and you find some who's into you. And sometimes you don't.