How Much Is Seventy Percent Off? (Calculating Percentages in Your Head)
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 seventy percent off, and a few more math tricks you can do in your head. You'll also find out where you can learn more about math 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 faster than a speeding shopping cart on your own, in your head.
No matter what your age, 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.
Watch This Video
In our explanation, we'll be using some of the information found in this video. It's just over 10 minutes long, but that will be time well spent to review or learn the basics of percentages, then practice to become familiar and comfortable with using this method of mental math.
To learn more than just percentages, take a look at more math videos from tecmath on YouTube.
The Easy Solution in Pictures
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Here's How to Calculate Seventy Percent Off in Your Head
Here's the long explanation, in words. There's actually two ways to do it.
Did you watch the video above? If you did, you've probably already solved your 70% off problem. If not, here's our explanation.
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 percent 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 percent?
To calculate 70% of $250, use the method described in the video above to figure 50% + 10% + 10% (which add 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 back one place to determine 10% of 250, which gives us 25.
So we get 125 + 25 + 25 which equals 175. So, now we know that 70% of $250 is $175. But we want to know what is 70 percent OFF of $250, so to get that answer we subtract $250 - $175 which equals $75. Not 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? Here's how we do it:
To calculate 30% of $250, think 10% + 10% + 10% adds up to 30%. We move the decimal back to the left to get our 10%, so 25.0 is 10%. Then 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 of "70 percent off of $250" is the same as "30% of $250." 3 x $25 = $75. That's the sale price and wow, what a bargain!
What is a percent, anyway?
Percent simply means parts out of hundred.
Per - cent
Parts out of - one hundred
One penny out of a dollar is 1 percent.
Using 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 seventy percent 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.
More Mental Math Videos
I like this teacher. His voice is kind and his math methods are magical!
You'll need to know how to multiply when you calculate percentages and his videos will help teach you shortcuts to make multiplication quicker. There's also a subtraction video here. You'll love the time-saving methods for working with numbers that you'll learn here.
© 2014 Susan Deppner