Hello everyone! My first post in this seemingly wonderful forum! Anyways, I an currently an undergrad and throughout my high-school career, I have honed my problem-solving skills very well. I have done very well on the olympiads, Putnam, IMC etc. Now that I am an undergrad, I still believe that solving problems is the best way to become better at problem solving. Can anyone recommend me math books with lots and lots of tough undergrad-level olympiad type problems, rather then just basic computational (plug-and-chug) exercises? Mainly for math, but physics/bio/chem/EECS would also be greatly appreciated. Thanks everyone!