By selling an article at $$\frac{3}{4}$$ of selling price, a trader incurred a loss of 10%. The Profit/loss percentage, when it is sold at the original selling price, is = ?

$$\eqalign{ & {\text{Let cost price of the article}} = 100 \cr & 10\% \,{\text{loss}} \cr & {\text{Therefore}}\,S{P_1} = 100 - 10 = 90 \cr & \frac{{{\text{Original Selling Pric}}{{\text{e}}_2}}}{{{\text{Reduced Selling Pric}}{{\text{e}}_1}}} = \frac{4}{3} \cr & 3{\text{ units}} = 90 \cr & {\text{1 unit}} = 30 \cr & {\text{4 units}} = 30 \times 4 = 120 \cr & \therefore {\text{Profit }}\% = \frac{{20}}{{100}} \times 100 \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 20\% \cr} $$