i sold a book at a profit of 10 % . had i sold it for $ 100 more , 15 % would have been gained . find the cost price ?
"115 % of cost - 110 % of cost = $ 100 5 % of cost = $ 100 cost = 100 * 100 / 5 = $ 2000 answer is a"
divide(multiply(divide(multiply(100, 10), subtract(15, 10)), const_100), 10)