# Percentage

[https://en.wikipedia.org/wiki/Percentage](https://en.wikipedia.org/wiki/Percentage)

* A percentage is a number or ratio expressed as a fraction of 100
* It is often denoted using the percent sign, `%`.
* A percentage is a dimensionless or pure number.
* 45% (read "forty-five percent") = 45/100 = 45:100 = 0.45
* Percentages are often used to express a proportionate part of a total.
* the term "percent" is derived from the Latin _per centum_ "by the hundred"
* the percent symbol evolved by gradual contraction of the Italian _per cento_ "for a hundred". "per" was often abbreviated as "p." and eventually disappeared; "cento" was contracted to two circles separated by a horizontal line, which evolved into the modern symbol.

Parts per $$10^i$$ where $$i=\{2,3,4\}$$

* $$\%$$ indicates parts per hundred, $$10^2$$ % (percent), ﹪ % ％
* $$‰$$ indicates parts per thousand, $$10^3$$ ‰&#x20;
  * spelled: per mil, per mill, permil, permill, permille, promille
* $$‱$$ indicates parts per ten thousand, $$10^4$$ ‱
