if a ' s salary is 20 % less than b ' s salary , by how much percentage is b ' s salary more than a ' s ?
"required percentage = [ 100 * 20 / ( 100 - 20 ) ] % = 25 % answer is a"
divide(subtract(const_100, subtract(const_100, 20)), divide(subtract(const_100, 20), const_100))