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Reprint edition published in April 2020.

Reading Level: 13-45 years

"Hard-to-solve" doesn't mean you need to know any higher math to do the puzzles in this book. There are no prerequisites of differential calculus, functional analysis, linear algebra, or anything like that, But while the puzzles don't require advanced mathematics to state, they do require insight to solve: How can you divide a regular pentagon into five identical pentagonal shapes? What is the only decade in American history to contain four prime-numbered years? What three right triangles with integer sides have areas numerically equal to twice their perimeters?

If you don't see the answers just yet, don't give up.

Remember, you have plenty of company. But if you come up with the right insight and solve the puzzles, you'll have a satisfaction you won't forget. This is one book that you'll be proud to carry around.

This book wouldn't have been possible without the work of some giants in the field. The author extends his thanks to everyone who showed how much fun puzzles are, from 19thcentury greats Sam Loyd and Henry Dudeney all the way to Martin Gardner. The work of Joseph Madachy, Leo Moser, Harry Nelson, Arlet Ottens, Richard Stanley, and other topnotch puzzle makers and solvers has also had a great influence. Rob Blaustein suggested some interesting puzzle concepts. Fraser Simpson provided timely and thorough proofreading. Last but not least, my editor Peter Gordon put everything together into a tidy little book. Thanks to all.