+1 for The Trachtenberg Speed System of Basic Mathematics. I remember learning that system decades ago, and have always kicked myself for lending my copy of the

+1 for The Trachtenberg Speed System of Basic Mathematics. I remember learning that system decades ago, and have always kicked myself for lending my copy of the book. I never got it back, and have stopped lending any books I value no matter who. Funnily, after applying the Trachtenberg system for many years, I came to realize the traditional methods were pretty good too.