Book excerpt: Perfect for anyone young or old looking to sharpen their mental math skills, these fast and fun puzzles are designed to rejuvenate and stimulate the mind. A range of difficulty levels—from beginner to advanced—are included, making this a suitable collection for all ages and abilities. With puzzles that include simple addition and substraction as well as more challenging problems involving percentages, fractions, and square roots, these are the ultimate brain-training tools for people on the go and anyone who wants to expand their mental agility.