I'm taking courses of math at university level, it's kind of the equivalent of master degree in mathematics, I'm from Argentina. The way to learn mth in my university is this: We attend lectures, we also do exercises, we also read at home. This question is about this: How do you "store" the exercises you solve? I have solved, many, many problem sets (as every math student in the world) I will describe my current system, I would be interested in knowing other systems you employ and what you think it's the best. My current method is I print the problem sets, I number the pages of my notebook, when I solve an exercise I write on a notebook, then I write the page number (and the notebook number, because I have tens of notebooks) ritght on the problem statement, on the problem set page.
This method is good, but there are books I don't print, and there are exercises on these books, and I can't write the books, because they are virtual ebooks. This is frustrating because, I will not remember I have solved that exercise.
I need a system that keeps track of every exercise, including books i don't print.