I believe everyone can learn mental math. In this short book, I am going to share 10 simple rules on how mental math works in practice. Unlike many other books, I will not burden you with tons of exercises. Rather I will give you several tricks you can use right there. For some tricks, I will teach you method that you can calculate quickly. In computer science, those are called the "algorithm." e.g. Trick 1 "Squares of number ended with 5" gives you an impressive party trick such that you can calculate the squares of two or even three digit number instantly. In some cases, I tell you the...