Real-Life Mental Math

I've written several articles in the past describing various mental math techniques you can use on the GMAT. The central point is this: The GMAT doesn't intend to test your arithmetic skills, so most calculations are simple enough to do in your head...if you have the practice.

Practice, conscious or not, is what separates those who are really good at mental math from everybody else.

You can improve your mental math skills by making piles of flashcards, or by forcing yourself to calculate in your head while doing GMAT problems. (In fact, I encourage the latter, if not the former.)

But even better practice comes in context. That is, instead of limiting mental math to the world of the GMAT, let yourself work on your arithmetic skills all the time. For whatever reason, I spend a lot of time tinkering with numbers in my head--and I've been doing it for as long as I can remember--and that does a whole lot more for my "number sense" than any book I've read or technique I've learned.

Contexts For Mental Math

The most obvious place to do some calculator-free calculations is the shopping mall. If you see an item that's 20% off, try to come up with the discount price in your head. Or, if your state sales tax rate is 8%, see if you can estimate the sales tax on your purchase before the clerk rings it up.

The kitchen is another great venue. If you cook from a recipe, you often have to change the amounts to fit the right number of servings, or you need to convert one unit of measurement to another. Rather than guessing, see if you can come up with the appropriate numbers.

One more: Do some arithmetic while exercising. Yesterday, I spent 30 minutes on the treadmill. Periodically, try to determine what fraction of your run (or bike ride, or whatever) you've completed, or perhaps your average speed.

Numbers are everywhere. A huge chunk of the GMAT Quantitative section consists of word problems--not exactly real-life scenarios, but close. If you can apply mental math techniques to the random occurences and habits in your own life, you are that much closer to making the connections between your skills and the questions you'll see on the test.

Best of all, mental math is a valuable skill for life, not just the GMAT. You may never be able to impress your friends with fast-calculating parlor tricks, but I promise you that practice--especially in context--will make you faster and more accurate.

About the author: Jeff Sackmann has written many GMAT preparation books, including the popular Total GMAT Math, Total GMAT Verbal, and GMAT 111. He has also created explanations for problems in The Official Guide, as well as 1,800 practice GMAT math questions.

• Mental Math: more articles
• All articles at GMAT Hacks
• Search GMAT Hacks

Total GMAT Math The comprehensive guide to the GMAT Quant section. It's "far and away the best study material available," including over 300 realistic practice questions and more than 500 exercises! Click to read more.