A trader marked the selling price of an article at 10% above the cost price. At the time of selling he allows certain discount and suffers a loss of 1%. He allowed the discount of ?

Let the cost price of an article = Rs. 100
Marked price of an article = Rs. 110 (10% above)
Selling price of an article = Rs. 99 (10% discount)
$$\eqalign{ & {\text{Difference}} = {\text{ }}110 - 99{\text{ }} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{ = Rs}}{\text{. 11}} \cr & {\text{Discount}} = \frac{{11}}{{110}} \times 100 \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 10\% \cr} $$