The marked price of an article is 50% above cost price. When marked price is increased by 20% and the selling price is increased by 20%, the profit doubles. If original marked price is Rs 300, then the original selling price is:
Joseph bought two woollen jackets for Rs. 2,100 and Rs. 3,150, respectively. By selling the first at a gain of k% and the second at a loss of k%, he found that the selling price of both is the same. What is the value of k?