Percentages are everywhere — they’re used in surveys, sales tax and to predict the chance of rainy days. But what is a percentage? How do you calculate percentages, and how do you convert percentages into decimals when the need arises? Let’s take a look.
What Is a Percentage?
Before we can learn to easily convert percentages, it’s worth breaking down exactly what a percentage is.
Start by looking at the word “percent”. Split it up and it is “per cent” — the cent here means century, but it’s also like the number of “cents” in a dollar: 100. Whenever you write a percentage, what it really means is “X per 100” — so 40 percent would be 40 per 100, or like saying that something happens 40 times out of every 100.
Now let’s look at finding percentages — how do you easily calculate percentages or deal with them if they appear in equations?
Let's start with an example. If you need to find 10 percent of a number, since that means one tenth of the number, you can simply divide the number by 10.
, which is
Let's try a more difficult example.
Solution: We know that
percent is the same as
, which means that we just need to divide
, which gives
. And using the rule above, we know that
Converting Percentages to Decimals
Sometimes it is necessary to convert a percentage to a decimal. This is helpful if you come across percentages inside a math expression, such as
. For the percentage term, simply move the decimal two places to the left, and you can simplify the problem.
Example: Simplify the expression
, which yields
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