Two excellent books on the subject are Secrets of Mental Math by Arthur Benjamin (for beginners) and Dead Reckoning: Calculating Without Instruments by Ronald D

Two excellent books on the subject are Secrets of Mental Math by Arthur Benjamin (for beginners) and Dead Reckoning: Calculating Without Instruments by Ronald Doerfler (more advanced). The Mind Your Decisions blog (http://mindyourdecisions.com/blog/tag/mental-math/ http://mindyourdecisions.com/blog/tag/mental-math/) has a lot of neat mental math tricks, but they're not really organized into a unified presentation there as in the books above.