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Percentage calculations without a calculator

Percentage calculations become much easier when we understand that they are multiplication calculations. You can put the numbers to be calculated in a different order. You can also separate the tens and hundreds into their own numbers.

When calculating a percentage of a number, you can easily calculate the numbers the other way around. Let's say you need to calculate 18 percent of 50. You can reverse the numbers and calculate 50% of 18. This makes it easier to see that the answer is 9.

Percentage calculations are multiplication calculations: you can calculate the number and the percentage in reverse

Percentage calculations are multiplication calculations. In multiplication calculations, you can easily reverse the numbers you are multiplying. Or, if there are more numbers, you can calculate them in any order. Two baskets, each containing three apples, have the same number of apples as three baskets, each containing two apples. A rectangle with sides of 2cm and 3cm has the same area as a rectangle with sides of 3cm and 2cm.

Let's look at the percentage problem: How much is A% of B? The answer can be found in the formula:

A% * B

We know that % is the same as one hundredth, or 0.01. This gives us:

A * 0.01 * B

Multiplications can be written in any order, so:

B * 0.01 * A

From which we can see that this is the same as:

B% * A

That is, B% of A.

You can remove two zeros and the percent from a percentage problem

In a similar way, tens or hundreds can also be removed as their own numbers and placed anywhere.

Let's take the problem: How much is 24% of 20. Let's develop this in the same style:

24% * 20 = 2 * 10 * 24 * 0.01 = 2 * 2.4 * 10 * 10 * 0.01

From that 10 * 10 * 0.01 is 1, or 100%, and what remains is:

2 * 2.4 = 4.8

So 24% of 20 is 4.8.

Above, we also notice that 10 * 10 and the percentage cancel each other out, or they result in 1, which does not affect the final result.

Examples of percentage calculations

With these lessons, we can now list some examples of making percentage calculations easier.

What is 8% of 50?
By reversing, we get 50% of 8, which is 4.

What is 12% of 25?
By reversing, we get 25% of 12, or a quarter of 12, which is 3.

What is 15% of 60?
We remove the zeros and the percent, and we get 6 * 1.5, which is 9.

What is 11% of 30?
Both numbers can be divided by ten while taking away the percent. This gives us the answer 3 * 1.1, which is 3.3.

What is 200% of 3.7?
Let's remove two zeros and the percent and get 2 * 3.7, which is 7.4.

What is 7% of 300?
Let's remove two zeros and the percent and get 3 * 7. So the result is 21.

What is 19% of 720?
Let's try this too. Let's remove two zeros and the percent and get 19 * 7.2. If we first calculate 20 * 7.2, we get 144. We can subtract 7.2 from this and get 136.8. This wasn't exactly easy, but it's not impossible. And practice makes perfect!

It's definitely worth trying to calculate percentages without a calculator, as the skill develops with practice. You can use the calculations and laws above as a guide. And of course, you can always use the percentage calculator to help you.

Author:

Arkikoodi

Published: 26.11.2024