Reading the description of the Mathematics skill, 1 rank is necessary for counting and basic math, and more gets into higher education.
The question, then, is why isn't that on the Adolescent Skill Ranks table? The suggestion would be to add it in :p It seems like a useful background skill that most cultures in most sci-fi settings (post apocalyptic need not apply) would have at at least 1 rank, some at even up to 3 or 4, I would think.
Laz