Self-published (to keep the cost low) through KDP Print (2018), 200 pages.
Intended audience: Advanced high school and beyond.
View on Amazon
(The Kindle version is a static-page “Print Replica” – basically a pdf in Kindle form.)

This book is a collection of 57 very difficult math problems with detailed solutions, along with many extensions and variations, that I have compiled over the years. Many of the problems appeared on my old Problem of the Week webpage. I finally (re)polished a number of those, added some new ones, and created this book. The problems are mostly classics that have been around for ages. They are divided into four categories: General, Geometry, Probability, and Foundational. (Cover illustration: Maki Naro)

Back cover (concise description of book)
Preface
Chapter 1 (all of the problems)
Corrections/typos/errata/clarifications

Side note: If you know of any middle school or high school students (or eager elementary school students) who are learning algebra, they might enjoy my new Algebra book!