How Much Is 70 Percent Off? (Calculating Percentages in Your Head)
Are You Stuck on a Percentage Problem?
Seventy percent off is almost always a bargain if you're shopping. But it's good to know how to calculate percentages in your head (or even on paper) so you'll know for sure if you're getting a good deal. And if you're taking an important math test, well, you really need to know how to work with percentages.
In this article, you'll learn how to calculate percentages, including 70% off, and you'll discover a few more math tricks you can do in your head. So, the next time you come across a sale or a percentage problem, you'll be able to amaze your friends (and yourself) by figuring out the solution—calculating percentages in your head faster than a speeding shopping cart.
No matter what your age is, if you have a working knowledge of basic math, you can learn math tricks and shortcuts to make calculating percentages and doing other mental math easy.
What is a percent, anyway?
"Percent" simply means "parts out of one hundred."
(per = parts out of; cent = one hundred)
For example, one penny = one cent coin, so one penny out of a dollar is 1%.
First, Review the Basics of Percentages
In our explanation, we'll be using some of the information found in the video below. It's just over 10 minutes long, but that will be time well spent reviewing or learning the basics of percentages, as well as practicing to become familiar and comfortable with using this method of mental math.
Step-by-Step Instructions for Calculating 70 Percent Off
Did you watch the video above? If you did, you've probably already solved your 70%-off problem. If not, here's the step-by-step explanation. There are actually two ways to do it.
First, make sure you're asking yourself the right question. If you need to know "What's 70% off?", then what you're actually asking yourself is, "What's 30% on?" Let me explain:
Let's say we're working with $250. We want to know what's 70% off of $250. Well, do we really want to know how much we're going to take off or how much is left after we remove that 70%? Either way of looking at the problem is okay, though one option is a little simpler than the other.
Method 1: Figuring Out 70% of $250 (How Much You're Saving)
- To calculate 70% of $250, first figure 50% + 10% + 10% (which adds up to 70%), because those numbers are really easy to work with. So, 50% (or half) of 250 is 125; then we move the decimal to the left one place to determine 10% of 250, which gives us 25.0.
- We get 125 + 25 + 25, which equals 175. Now we know that 70% of $250 is $175. That's how much you're saving!
- However, we want to know what is 70% OFF of $250, so to get that answer, we take one more step. Subtract $250 - $175, which equals $75. That's how much you're spending.
This isn't difficult math, but there's an easier way. Since we know that when we subtract 70% from 100%, we have 30% left, the amount we're actually looking for is 30% of $250. In other words, we're saving 70% but spending 30%, and we really want to know how much we're going to spend. So why not calculate that in the first place?
Method 2: Figuring Out 30% of $250 (How Much You're Spending)
- To calculate 30% of $250, think about how 10% + 10% + 10% adds up to 30%. We move the decimal back to the left to get our 10%, so 25.0 is 10%.
- Next, we either add 25 + 25 + 25 OR we multiply 25 x 3. In either case, we get our answer: $75. That's much quicker and easier than working with the 70% and having to take an extra step to subtract.
So, the bottom line is that "70% off of $250" is the same as "30% of $250." 3 x $25 = $75. That's the sale price—and wow, what a bargain!
A Visual Example of the 30 Percent MethodClick thumbnail to view full-size
How to Calculate Percentages With a Calculator
There's more than one way to calculate a percentage. If you have a calculator, you'll need to structure the problem a little differently from the way we did it above.
To calculate 70% off on a calculator, think "250 minus 70% equals what?"
Using the calculator, enter the starting number (250 in our example), then the minus sign, then 70 followed by the % key, then the = key to get the answer.
250 - 70% = 75
More Mental Math Videos
To learn more than just percentages, take a look at the other math videos from tecmath on YouTube. You'll need to know how to multiply when you calculate percentages, and this instructor's videos will help teach you shortcuts to make multiplication quicker. There's also a subtraction video. I like this instructor—his voice is kind, and his math methods are magical! You'll love the time-saving tips for working with numbers that you'll learn here.
How did you feel about math when you were a student?
© 2014 Susan Deppner