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# How to Use Percentages to Easily Calculate Sales Prices Learn how to use the power of ten percent to quickly and easily calculate how much money a sale will save you.

By
Jason Marshall, PhD
Episode #13 In the last article, we applied our knowledge of fractions to begin making sense of percentages, and we used this new tool to quickly and easily calculate how much to tip at restaurants…all in our heads! Today, we’re continuing our exploration of percentages by using the power of 10% to quickly calculate how much money you’ll save the next time you go shopping for sales.

## Review of How to Calculate Ten Percent

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Before we get into calculating how much you can save at a sale, let’s briefly review how to easily calculate 10% of any amount of money. For example, what’s 10% of \$144? First, write the amount out with the decimal point and the digits representing the number of cents—like you’d see on a cash register: \$144.00. Then, to find 10% of that amount, just move the decimal point one position to the left. So, \$144.00 becomes \$14.40 and, therefore, 10% of \$144 is \$14.40.

If that makes sense, then you’re ready to move on. If you want a little more practice first, check out the practice problems from the end of the last article. And then be sure to catch the Math Dude Video Extra! episode on YouTube or Facebook to watch me solve the problems.

## How to Use Percentages to Figure Out How Much You’ll Save at a Sale

Once you can calculate 10%, figuring out how much you’ll save when things are on sale is easy. For example, say you’re looking at a sweatshirt that has an original price of \$40, but is advertised at 30% off. What’s the new price? Well, just as with calculating tips in the last article, start by finding 10% of \$40. Moving the decimal point one place to the left in \$40.00, we find that 10% of \$40.00 is \$4.00. So, 30% of \$40 must be three times as large since 30% = 3 x 10%. In other words, 30% of \$40 is 3 x \$4, which is \$12.

So, what’s the final price? What do we do with this \$12? Well, since we’re talking about a \$12 discount here, the final price had better be less than the initial price. So, to get the final price, just subtract the savings, \$12, from the original price: \$40 - \$12 = \$28.

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