That's a question I NEVER ask, because you never wanna know the answer to it. Hell, the girl could say "Two" and it might have you feeling some type of way, or you simply won't believe her... which brings me to the other point - no matter what the answer, you're not going to believe them anyway (men or women) so what's the point?
I don't think I'd really have a problem with it anyway as long as it wasn't a ridiculous amount. It's a better likelihood that I'd have a problem with a specific man she fukked if I knew that person.