I bought this book because I got a performance note at work saying that I needed to work on my math skills.  As an accountant, I'm really good with Excel and my trusty calculator.  However, mental math can come in really handy if you're on the phone with a client or in a boardroom and you don't have your computer nearby.  I found that adding &amp; subtracting left to right is much easier, and even though it takes a little practice to get comfortable with the techniques in the book, if you work through the exercises it really works.  I think it's invaluable.  Yeah, there's a chapter on tricks to impress your friends (um, nerdy, I would NEVER pull those out at a party), but I didn't even bother reading that and skipped right to improving my mental math.  Easy to read, fun, and it works.  Definitely recommend it.