Hard-To-Solve Math Puzzles

As an avid collector of puzzle books, I can honestly say that *Hard-to-Solve Math Puzzles* by Derrick Niederman is one of the best puzzle/Mensa-type books I have come across. What is unique about this book is that this book concentrates on clever mathematical puzzles requiring only a high school-level of math knowledge.Most other puzzle books on the market: mix math questions with other types of puzzles (like word puzzles), require knowledge of math that is way too advanced for most run-of-the-mill puzzle fans (e.g, math olympiad type books or books requiring university-level math), or avoids math altogether. Niederman's book is focused in on math puzzles that are challenging but doable for most puzzle fans.Another thing that I liked about this book is that the problems are truly challenging (but do not require advanced math knowledge). Niederman's problems usually require more insights and sophistication than comparable problems by other respected puzzle makers.Finally, this book is endorsed by Mensa, a plus for people who want a seal of approval.