by selling 10 pens for a rupee a woman loses 18 % . how many for a rupee should he sell in order to gain 30 % ?
"d 82 % - - - 10 130 % - - - ? 82 / 130 * 10 = 6"
inverse(add(divide(divide(const_100, subtract(const_100, 18)), 10), divide(multiply(divide(divide(const_100, subtract(const_100, 18)), 10), 30), const_100)))