Short-Cut Math Gerard W. Kelly

Clear, concise compendium of about 150 time-saving math short-cuts features faster, easier ways to add, subtract, multiply, and divide. Each problem includes an explanation of the method, a step-by-step solution, the short-cut solution, and proof, as well as an explanation of why it works. No special math ability needed. Это и многое другое вы найдете в книге Short-Cut Math (Gerard W. Kelly)