I am currently self-studying Calculus by Spivak. I did the first few chapters a while ago, then had to stop for a while because I took a heavy course load over the summer. Now I have more free time, and currently on chapter 5 (Limits). Now, I have the fourth edition, so there's usually between 20 and 40 problems a chapter, and sometimes much more. I don't think it's realistic to do every single problem, considering their difficulty and the time it takes to solve them. But on the other hand, I want to make sure I'm building up a solid mathematical foundation by getting lots of practice. So, for those who have studied from Spivak, approximately what percentage of problems would you recommend I do? I have been making sure to do more problems when I struggled with a chapter at first - for example, I had a lot of trouble with limits and epsilon-delta proofs at first, so I've been doing almost every problem in Chapter 5. But if I want to finish working through the book in the foreseeable future, I'm not sure I can do that for every chapter.