Scientific American presents Math Dude by Quick & Dirty Tips. Scientific American and Quick & Dirty Tips are both Macmillan companies.
Today we're turning our attention to solving math problems faster than you ever thought was possible. In this article you’ll learn two tips to help you add quickly…all in your head! Next we'll build on these tips to learn another way to do some fast addition in your head.
Tip #1: Find Pairs of Numbers that Add to 10
Here is perhaps the single most useful quick and dirty tip to help you calculate quickly: When adding a list of numbers, look for pairs of numbers that add to ten.