Figuring the Joy of Numbers

Although the whole book is excellent, the multiplication chapter is the crowning achievement. Shakuntala teaches you how to cross multiply any two numbers in a very simple, straightforward way that is easy to learn and easy to do. And if you already know how to do Chisanbop (Fingermath), you will have a very powerful tool to do large multiplication problems without paper or pencil. She also does a ton of good stuff with all the other basic arithmatical operations. An great book that should be part of anyone's math library.