Problems for Mathematicians, Young and Old (Dolciani Mathematical Expositions)

Rating:
Summary: sublime problems although some are sophisticated
Review: I would put this book above the puzzle books by Martin Gardner. The problems range in prerequisite knowledge from none required (brain teasers and logic puzzles) to undergraduate degree in mathematics (topology, calculus). I especially recommend it for someone who likes good brain teasers (like the three light switches puzzle) but also knows some complicated math.