The cost of two articles is the same. One article among them is sold at a profit of 15% and the other is sold at a profit of 12%. If the difference between their selling prices is Rs.18, what is the cost of each article?

Let the cost of each article be Rs. x. Selling price at 15% profit is 1.15x, and at 12% profit is 1.12x. The difference (1.15x - 1.12x) = 0.03x equals Rs.18. Solving: 0.03x = 18, so x = 18 / 0.03 = Rs.600. We can verify: 15% of 600 = 90 (SP = 690), 12% of 600 = 72 (SP = 672), and 690 - 672 = 18. This matches the given condition.