Arithmancy a science having to do with numbers (similar to numerology) is taught at Hogwarts for third-years and up. However, this subject is optional.
Arithmancy sounds a lot like arithmatic which is the older word used for math.
Arithmancy teaches the magical properties of numbers, and the relations they have in the magical world. It is a useful subject for magical inventors of spells, artifacts and potions, and is a more accurate and reliable method of attempting to predict future events.
As for traditional maths, the wizarding community does not have any form of primary schools, at least in Britain, so it is up to wizarding parents to teach thier children how to read, write, do maths, and so forth. It was once implied that Crabbe and Goyle are illiterate, unable to read or write. This was in the Chamber of Secrets movie, however, not the book, so it is debatable weather or not it is canon.
The Gaunt family, being entirely uneducated, were very likely illiterate.