robert ' s salary was decreased by 20 % and subsequently increased by 20 % . how much percentage does he lose ?
"let original salary be $ 100 salary after decreasing 20 % = 100 - 100 x 20 / 100 = $ 80 salary after increasing 20 % on $ 80 = 80 + 80 x 20 / 100 = $ 96 percentage of loss = 100 - 96 = 4 % answer : a"
multiply(divide(subtract(multiply(const_100, const_100), multiply(subtract(const_100, 20), add(const_100, 20))), multiply(const_100, const_100)), const_100)