by selling 15 pens for a rupee a woman loses 25 % . how many for a rupee should he sell in order to gain 25 % ?
"d 85 % - - - 15 125 % - - - ? 85 / 125 * 15 = 10"
inverse(add(divide(divide(const_100, subtract(const_100, 25)), 15), divide(multiply(divide(divide(const_100, subtract(const_100, 25)), 15), 25), const_100)))