The term "percent" (also written as "per cent") is derived from the Latin word "per centum", which means, "by the hundred". Indeed, a [b]percentage[/b] expresses a ratio, which is expressed as a fraction of 100. Mathematically speaking,[br][br][math] \large 1\%=\frac{1}{100},[/math][br][br]that is,[br][br][math] \large 1\%=0,01.[/math][br][br]Using this definition, we can convert percentages to decimal numbers, or vice versa.

Convert 0,072 and [math]\frac{3}{4}[/math] into percentages.[br][br][b]Solution:[/b] To convert decimal numbers into percentages, we multiply by 100. This principally moves the decimal separator two steps to the right. Therefore,[br][br][math]\large 0,072=0,072\cdot100\%=7,2\%. [/math][br][br]To convert [math]\frac{3}{4}[/math] into a percentage, we first convert the fraction into a decimal number. That is, [math]\frac{3}{4} = 0.75[/math]. Finally, we multiply the decimal number by 100:[br][br][math]\large \frac{3}{4} = 0,75 = 0,75 \cdot 100 \% = 75 \% .[/math]

Convert 42,3% and 0,12% into decimal numbers.[br][br][b]Solution:[/b] To convert percentages into decimal numbers, we divide by 100. This principally moves the decimal separator two steps to the left, so[br][br][math] \large 42,3\% = \frac{42,3}{100} = 0,423 . [/math][br][br]Similarly,[br][br][math] \large 0,12\% = \frac{0,12}{100} = 0,0012 . [/math]