An article was sold at 10% profit. If it had been sold at Rs 26 more than the selling price, the profit would have been 15%. The cost price of the article is:

The cost price is Rs 520.

The extra Rs 26 raises the profit from 10% to 15%.

So Rs 26 equals the 5% rise on the cost price.

5% of cost = 26.

Cost = 26 / 5 x 100 = Rs 520.