a watch was sold at a loss of 15 % . if it was sold for rs . 400 more , there would have been a gain of 5 % . what is the cost price ?
"85 % 120 % - - - - - - - - 25 % - - - - 400 100 % - - - - ? = > rs . 1600 answer : a"
divide(multiply(400, const_100), subtract(add(const_100, 5), subtract(const_100, 15)))