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How to calculate a percentage

Express numbers differently!

Everyone’s brain processes information [taken from the world] differently, and it is no different when it comes to mathematical matters. One of us will be impressed when a friend boasts that he earns 60,000 Polish złoty a month, while another will be astonished when s/he hears that it is more than 1,000% of the national average. By knowing how to calculate percentages, you can clearly communicate data to your audience.

When do we work with percentages?
With percentages, we can easily express the relationship between numbers. To calculate them, we use our knowledge of fractions: 1% = 0.01, and in some cases an equation with an unknown. There are three basic situations in which we can be tasked with calculating a percentage:

1. calculating the percentage of a given number
2. calculating a number based on a percentage
3. calculating what percentage of a number is another number

Specific tips on how to calculate a percentage
In the first situation, to calculate the percentage of a number, we multiply the number by the percentage previously converted to a fraction. For example, to calculate 2% of 60, we would do it as follows: 2%*60 = 0.02*60 = 1.2
That's it! Now you know how to calculate the percentage of a number.

The second situation additionally requires the introduction of an unknown. For example, knowing that 20% of a number is equal to 15, we write it down as follows:
0.2*x=15 //: 0.2
We have found the number we are looking for, which is 75.

The third situation is when we need to find out what percentage of a number is another number. In the problem: there are 5 white balls and 15 black balls, calculate what percentage of all the balls are white balls, we use the following method:

firstly, we calculate how many balls there are (5+15=20),
write down the relation of white balls to all balls in a simple fraction (5/20) and then multiply the fraction by 100% (5/20*100% = 25%).

The basic mathematical knowledge of how to calculate percentages described above is useful throughout life, not only at school. However, if we are not sure of the accuracy of our calculations, it is worth using a percentage calculator.


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