Where did the percent sign (%) come from?

It makes no sense mathematically --- you can't divide by zero. So why do we show percentages (hundredths) with a mathematically invalid symbol: %  Zero divided by zero? The interesting Shady Characters The secret life of punctuation blog has an answer. And, as usual, human laziness is the mother of linguistic invention: Originally written out as per cento (“per hundred”), the phrase was eventually abbreviated to p cento, and then to pco, but written as a stylized symbol made up of a p; a c with a long, sweeping end stroke; and a superscript o. You can see it here: the circled amount is 10%. Full story/better explanation:  Shady Characters The secret life of punctuation: Miscellany № 59: the percent sign