This is a very entertaining book, well produced with a balance of easy and not so easy puzzles, sorted in increasing difficulty order. If you are familiar with the idea of solving those type of puzzles, the first 75 to 80 goes smoothly and the last 20 to 25 are more challenging. Overall I would say that you should allocated around 3 hours to be able to solve all 100. I just could not figure out the logic for the "ring" puzzles (there are 2 or 3 of those kind...), but that was just me. I recommend this book to anyone who wants to have fun exercising your brains while waiting for someone or in any spare time you might have when you are doing nothing. ( )