A shopkeeper sold an article at a profit of 30%. If both the cost price and selling price are lowered by Rs. 100, then the profit would be 4% more than before. Then find the cost price of the article?

Let CP = x. Original SP = 1.3x. New CP = x-100, new SP = 1.3x-100. New profit = (1.3x-100) - (x-100) = 0.3x, which is 4% more than 30% of original CP. This means 0.3x = 0.34x, which is contradictory. Actually, new profit % = 34%, so (0.3x)/(x-100) = 0.34. This gives 0.3x = 0.34x - 34, so 0.04x = 34, x = 850. Wait: 34% is 4% more than 30%, not of CP.