I wouldn't care so long as the goal is that I'm the only one she'll be sleeping with moving forward. Why should I care how many people she's slept with before me? It seems irrelevant.
Naturally it's going to depend on the guy, but for me it's not that big a deal. I would interpret a bigger number as she simply is in tune with her sexuality and likes having sex. And since I like having sex, that would seem to be a non-issue. The number itself isn't as important as the details behind it, such as was any of it risky or unprotected sex, was she ever unfaithful, how long ago the last addition was, that sort of thing.