This compact book has rather deep problems, meaning they take scratch paper and maybe research, like revisiting Chinese Remainder Theorem, etc. I wanted this for what Lewis Carroll called "pillow problems" in The Mathematical Recreations of Lewis Carroll: Pillow Problems and a Tangled Tale. That is, conundrums to hold in one's head and drift off to sleep contemplating. For me, good ones help my repose and are better than Ambien or whatever. Well, most of these were too difficult for me for that. Though some were fine, including thankfully the last one to end on a high note. Also, and at my age this is important, the font was too small to read without my glasses which I don't like to take to bed. Though the book was small this was unnecessary as decorative illustrations take up most of each page.