I'm asking this because I have had moments in the past where, despite me asking for their number for very practical reasons, girls would simply deny saying stuff like "we have common friends" "there is facebook for contact" and stuff like that. Is this the norm or the exception? As in, if I provide a (even semi-)valid reason for her to give me her number, is it normal for her to look for other means of communication, or is it the norm for her to just hand over the number without any hassle at all?

They are excuses so they don't have to hurt your feelings

Of course, I have an example. There's this sort of classmate of mine(we only take certain classes together) and we got in a chat about one of our common professors(I found a really nice, hidden secret about him). In order for her to get the secret, I asked for her number(seeing as the secret was a link to something, I had to send it to her right away, and the only instrument at hand was my phone). She, without a second thought, asked me for my phone so she could write it down. I'm not really interested into her, so I'd just like a second opinion on this: could she be interested in only the link? Or (considering how easily she gave me her number) she could be somewhat interested?