*My friend Laura Laing has an awesome new book called Math for Grownups: Re-Learn the Arithmetic You Forgot From School…. As the mother of daughters in honors level math classes, I’ll do whatever I can to help promote the message that math skills *and* women can co-exist. It’s one of the reasons that we’re fans of Danica McKellar’s books about math, such as Math Doesn’t Suck: How to Survive Middle School Math Without Losing Your Mind or Breaking a Nail. Today, Laura is sharing with us a guest post about how you can use math tricks to remain true to your frugal mission. I know that on almost shopping trip I make to the supermarket, I’m doing algebra at some point during the trip. So math+grocery shopping=smart! Now onto Laura’s advice *

If you’ve started down the frugality path, you have probably already been smacked in the face with one unavoidable fact: there’s math involved in living within or below your means. For some, this is no biggie. For others, this could very well be the difference between saving a little and saving a lot.

But even if your basic math skills are rusty, you can handle these calculations, no problem. A few simple tricks will help you stay frugal and even take it up a notch!

**1. Learn the art of estimation.**

As a frugal person, you may be compelled to count each and every penny. And that’s a good thing. But many times, estimation is good enough. The important thing to consider is this: What’s the question? If you want to know if you can afford to buy something, careful estimation is probably the way to go. If you want to know how much you’ll save, go for an exact answer.

**2. Know your 1.5 addition facts.**

Okay, so you know your addition and subtraction facts by heart, right? But knowing that 1.5 + 1.5 = 3 and 2 + 1.5 = 3.5 can help you estimate costs more accurately and quickly. With these quick facts on hand, you can round prices to the nearest 50¢ before adding them. Then you’re closer to the actual price or savings than if you rounded to the nearest dollar.

**3.** **Practice with percents.**

Everyone has their own process for finding 10%, 20% or 50% of anything. But in case you’re feeling out of practice, here are a few ways to do the math in your head:

- To find 10%, move the decimal point
~~two~~one place to the left. - To find 20%, move the decimal point
~~two~~one place to the left and double the answer. - To find 50%, divide by 2.
- To find 25%, divide by 4.
- To find 15%, move the decimal point
~~two~~one place to the left and add half of that answer to the answer.

**4. Look at what’s missing.**

One of the reasons that math is so challenging in the real world is because of the way it’s taught in school. On a test or worksheet, you were usually given all of the information that you would need to solve a problem. Not so for everyday math. So, each time you’re faced with a real-world math problem, ask yourself, “Do I have all of the information?” Details like membership fees, gasoline and taxes may strip you of your savings, making another option the better deal.

*Laura Laing is the author of *Math for Grownups*, a funny, easy-to-understand and practical guide to the math that we do in everyday life. She blogs at **www.mathforgrownups.com**.*

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MelodyJ says

Thanks so much for this post. I will be trying out these tips because I need them.

PK says

No worries — the decimal move and x2 or x1.5 is how I calculate my tips — didn’t want any servers to get short-changed!! 🙂

Laura Laing says

Whoops! Yep, you are absolutely right. Oy. I’ll see if Leah can correct that in the copy, since it’s such a big mistake.

I need a proofer! *smile* Thanks so much for the heads up.

Laura

Leah Ingram says

Taking care of it now…

PK says

To get 10% (which affects almost all the other percentage calculations you’ve listed) wouldn’t you move the decimal just one place to the left?