a watch was sold at a loss of 10 % . if it was sold for rs . 500 more , there would have been a gain of 10 % . what is the cost price ?
"90 % 110 % - - - - - - - - 20 % - - - - 500 100 % - - - - ? = > rs . 2500 answer : c"
divide(multiply(500, const_100), subtract(add(const_100, 10), subtract(const_100, 10)))