I do not understand why nobody mentioned Schaum's Outline of Theory and Problems. These books offer a lot of practice in different branches of math. From algebra to calculus to differential equations,logic, topology,...

It has always been a great idea to practice my math skills with the problems there.

Another thing, I learned calculus I to III before getting in to univ from the book:

[CALCULUS: An introduction to Applied Mathematics by H.P. Greenspan (Author), D.J. Benney] 1 You will definitely find it in most university.

Also I learned Group theory (again before getting in to univ) from:

Algebra (2nd Edition) Michael Artin

My final remark: You will get high-quality math ebooks for free from the internet, a great repository of knowledge for everyone.