Problem: a pair of articles was bought for $ 50 at a discount of 50 % . what must be the marked price of each of the article ?
Rationale: "s . p . of each of the article = 50 / 2 = $ 25 let m . p = $ x 50 % of x = 25 x = 25 * . 5 = $ 12.50 answer is b"
annotated_formula: divide(multiply(subtract(const_100, 50), divide(50, const_2)), const_100)