1. **Stating the problem:** The cost of 10 articles equals the selling price of 9 articles. We need to find the profit or loss percentage. 2. **Let the cost price (CP) of one article be** $x$. 3. **Total cost price of 10 articles** = $10x$. 4. **Selling price (SP) of 9 articles** = $10x$ (given). 5. **Selling price of 1 article** = $\frac{10x}{9}$. 6. Now, compare SP and CP of one article: CP = $x$ and SP = $\frac{10x}{9}$. 7. **Profit per article** = SP - CP = $\frac{10x}{9} - x = \frac{10x - 9x}{9} = \frac{x}{9}$. 8. Profit percentage = $\left( \frac{\text{Profit}}{\text{CP}} \right) \times 100 = \left( \frac{\frac{x}{9}}{x} \right) \times 100 = \frac{1}{9} \times 100 = 11.11\%$. **Answer:** There is an 11.11% profit.