I'm going to cheat and combine a couple of books into "one book". The Manhattan Prep GMAT test prep math books were really good for me for everyday life. I lear

I'm going to cheat and combine a couple of books into "one book". The Manhattan Prep GMAT test prep math books were really good for me for everyday life. I learned a lot of shortcuts and quick heuristics to use and got better at estimating after going through those books. It doesn't help me "get better" in an academic sense, but those books pay dividends every day for me.