This book explores the art of estimation and mental calculation, demonstrating how to approximate answers to complex mathematical problems using simple tools and logic. The author, Rob Eastaway, guides readers through various scenarios, from calculating the number of cats worldwide to the probability of winning the lottery twice, emphasizing the power of human ingenuity over calculators. The text is enriched with anecdotes, quizzes, and practical tips, making the process of estimation both educational and entertaining.

The book is lauded by notable figures such as Simon Singh, who calls it 'another terrific book by Rob Eastaway,' and Hannah Fry, describing it as 'A delightfully accessible guide to how to play with numbers.' The reception highlights its engaging approach to mathematics, making complex ideas understandable and enjoyable for a broad audience. Readers are likely to appreciate its practical applications and the encouragement it provides for developing mental calculation skills.