How To Quickly Calculate Percentages In The Head?

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How often do you typically need to quickly calculate percentages in the head? With the development of technology like smartphones, calculators, etc., you’d think that you would never have to do this. However, such situations occur more often than you think, and there is often money involved.

Consider a situation in a supermarket or a store where you are choosing between two comparable products. One product has an offer of 63% off of its maximum retail price, and the other has an offer of 13% off. If the money involved is a lot, we typically take out our phones or calculators to do the math. But for everyday products, we just can’t be bothered.

With the decision to not bother calculating, we often leave money on the table. In the worst case, we get manipulated by complex pricing tactics. A little money left on the table every time accumulates to a considerable sum over long periods. That’s precisely where the skill to quickly calculate percentages in the head would come in handy.

In this article, I’ll be taking you through a step-by-step process of how to do this. We will be implicitly using algebra, but there is no algebra knowledge required from you to be able to do this. You will realise at the end of the article that it is much simpler than it appears to be. Let’s get started.

This essay is supported by Generatebg

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Know Your Splits

The first thing you will need is the ability to calculate the following percentages of a given number: 50%, 25%, 10%, 5%, and 1%. If you can do this, then you can pretty much calculate any percentage of a given number. Let us look at these percentages individually.

What is 50%? It is essentially half of the given number. Similarly, 25% is a quarter of the given number, or half of the half (50%). 10% of a given number is the number which you will need to multiply by 10 to get to the given number. In other words, you can calculate 10% by dividing the given number by 10. 5% is half of 10% (that we just calculated), and 1% is the value of 10% divided by 10 again.

If you find my words confusing, let’s look at an example to drive the point home:

To reiterate, all you’ll need to calculate any percentage of a given number is the ability to work out these five percentage numbers (50%, 25%, 10%, 5%, 1%) in your head. How does that exactly work? Let’s look at that next.

Quickly Calculate Percentages as Combinations of Splits

Once you have worked out the five percentage numbers, it is a fairly simple task. All you need to realise now is the following: any percentage can be expressed as a combination of these five percentage numbers.

This is the part where we implicitly use algebra. But worry not. Check out the worked-out examples below, and you will get it straight away!

Now that we have all the ingredients necessary to quickly calculate percentages in the head, let’s try out an example:

To demonstrate the procedure one more time, I’ll work out the question that I asked in the title image:

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Approximate for Speed and Convenience

You would have noticed that all of the examples that I have been working with so far are nice and rounded numbers. It is indeed true that such numbers are easier to work with. However, in real life, we see price tags reading “Save 15% from 1499!!” What should you do in such cases?

The answer lies in your purpose. If you aim to just compare products and make a decision, approximating 1499 with 1500 does not impact the outcome. Real life is no math Olympiad. We do not need more accuracy than we require.

So, the next time you are roughly comparing percentages at your workplace or the supermarket, you can try this method out. You will be pleased with how it enables you to make quick and efficient decisions!

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Further reading that might interest you: How To Run A Math Hotel With Infinite Rooms? and How To Multiply Any Number By 11 In The Head?