Like, questions that you would technically be able to solve with very limited knowledge of a particular subject, except that it requires more work/cleverness. For example in Calc I, I was able to solve every problem for each learned topic given in the textbook rather easily, however on the exams the questions were nothing of the easy nature in the textbook and as such were much, much more difficult and some students complained that they did not learn the material to solve these problems, when in fact they just required extremely tricky knowledge to break through them. Sometimes there are questions we haven't learned, but we are expected to learn some topics on our own due to the limited number of class hours. I have no complaints about that, as I believe in taking my own responsibility. So the textbook questions being too easy, are there any web resources for different subjects like maths/physics that list extremely difficult problems that don't require advanced knowledge of the subject and can realistically be solved/expected to appear on a lower-level undergraduate exam? What about Spivak's Calculus for the rest of my Calculus sequence? I'm told it's more of a Real Analysis book, but can it be used as a supplement for introductory Calc II/III courses, especially the problems in the book that might appear in a first year Calculus course?