Where did the % come from?

Answer 1

Generally agreed that the earliest form of the symbol was an Italian manusript from 15th century and that before this the expression "per cento" (the Italian form) was abbreviated in various ways, including "p cento". How the elements of this expression became the modern "solidus form" (so-called because the line between the o's now uses the slanted line called a "solidus") in place of a horizontal line between the o's is less certain.

It might have begun with a sideways P on top of "cento", the latter eventually shortened to "-o" (OR shortened to "c", which was then closed into a circle to make the two halves of the sign match).

For further explanation and pictures of older forms and how they may have developed see:
http://www.roma.unisa.edu.au/07305/symbols.htm#Percent
http://en.wikipedia.org/wiki/Percent_sign#Evolution
http://mathforum.org/library/drmath/view/58082.html

Answer 2

it came from math experts meaning /=1 the 2 oo =00 so % = 100