Now that we've learned the basics of lightning fast mental addition, mental subtraction, and mental multiplication, it's time to turn our attention to a few tips that will help you take your skills to ...

Calculators are awesome, but they’re not always handy. More to the point, no one wants to be seen reaching for the calculator on their mobile phone when it’s time to figure out a 15 percent gratuity.

The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their ...