books.google.com - This new, revised edition of the bestselling Speed Mathematics features new chapters on memorising numbers and general information, calculating statistics and compound interest, square roots, logarithms and easy trig calculations. Written so anyone can understand, this book teaches simple strategies...https://books.google.com/books/about/Speed_Mathematics.html?id=U8zG2cf0qHwC&q=units+digit&utm_source=gb-gplus-shareSpeed Mathematics