Two excellent books on the subject are <i>Secrets of Mental Math</i> by Arthur Benjamin (for beginners) and <i>Dead Reckoning: Calculating Without Instruments</i> by Ronald Doerfler (more advanced).<p>The <i>Mind Your Decisions</i> blog (<a href="http:&#x2F;&#x2F;mindyourdecisions.com&#x2F;blog&#x2F;tag&#x2F;mental-math&#x2F;" rel="nofollow">http:&#x2F;&#x2F;mindyourdecisions.com&#x2F;blog&#x2F;tag&#x2F;mental-math&#x2F;</a>) has a lot of neat mental math tricks, but they&#x27;re not really organized into a unified presentation there as in the books above.