How to calculate almost anything in your head.Did you know that it's easier to add and subtract from left to right, rather than the other way round?You can be taught to square a three-digit number in seconds. Learn how to perform lightning calculations in your head, discover methods of incredible memorisation and other feats of mental agility. Learn maths secrets for the real world, from shopping to calculating a restaurant tip and figuring out gambling odds (or how much you've won). Learn how to solve sudoku faster.