This book taught me to do maths in my head which is fantastic. We  have become so dependent on calculators that it limits our brain power and makes us feel that we cannot do mental math but this book proves us wrong. I use it as a reference guide all the time to revise the concepts. I plan to be a maths teacher soon and definitely will be using it in my classroom. I Absolutely love this book and thanks the author for sharing his brilliance. Everyone should purchase this book because it can be used in our everyday lives and is very essential.