EXACTLY! It's a math problem. And she invited this scrutiny as much as she invites stud-mares into her dorm room.
Boys and girls! The pill costs $XXX, condoms $YYY. Sheila uses both and spends $ZZZ. How many times a day is she getting laid?
Gosh, this is supposed to be a family friendly site. But unfortunately this topic has gotten thrust way out into the open, no dirty allusion intended.