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Update index.md (#19176)

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Created a draft guide for finding a percent. Also added info about arithmetical operations on percentages. (first pull request, so please forgive any errors).
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joesvetz
2018-10-15 21:58:05 -06:00
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@ -3,13 +3,35 @@ title: Finding a Percent
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## Finding a Percent
This is a stub. <a href='https://github.com/freecodecamp/guides/tree/master/src/pages/mathematics/finding-a-percent/index.md' target='_blank' rel='nofollow'>Help our community expand it</a>.
Percent literally means "out of a hundred" or "per hundred" ("cent" like century).
<br>A percentage is just a different way of writing a decimal. For example, instead of writing 0.25, we write 25%. Or instead of writing 1.4213, we write 142.13%.
<br>Percentages are created by moving the decimal point of a decimal two digits to the right and adding a percent sign (%) to the end of the number.
<a href='https://github.com/freecodecamp/guides/blob/master/README.md' target='_blank' rel='nofollow'>This quick style guide will help ensure your pull request gets accepted</a>.
#### Mathematical Operations with Percentages
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The simplest way to perform math with percentages is to first convert them to decimals, perform the math, then convert the result back to a percentage.
*Note: Addition and subtraction can be performed without any conversions.*
###### Addition Example
<pre>Consider the problem: 14% + 256%
Simply add the numbers leave the percent sign after the result: 14 + 256 = 270<u>%</u></pre>
###### Multiplication Example
<pre>Consider the problem: 28% * 133%.
1. Convert the percentages to decimals by moving the decimal point two spaces to the left (0.28 * 1.33)
2. Perform the mathematical operation as you would normally (0.28 * 1.33 = 0.3724)
3. Convert the result back into a percentage by moving the decimal point two spaces to the right (37.24%)</pre>
*Division would follow the same steps.*
#### More Information:
https://www.mathsisfun.com/percentage.html
https://www.khanacademy.org/math/pre-algebra/pre-algebra-ratios-rates/pre-algebra-percent-problems/v/finding-percentages-example
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