If there is a profit of 20% on the cost price of an article, the percentage of profit calculated on its selling price will be -

$$\eqalign{ & {\text{Let C}}{\text{.P}}{\text{. be Rs}}{\text{. }}x. \cr & {\text{Then,}} \cr & {\text{Profit}} = 20\% {\text{ of Rs}}{\text{. }}x \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {\text{Rs}}.\frac{x}{5} \cr & {\text{S}}{\text{.P}}{\text{.}} = {\text{Rs}}.\left( {x + \frac{x}{5}} \right) \cr & \,\,\,\,\,\,\,\,\,\,\, = {\text{Rs}}.\frac{{6x}}{5} \cr & \therefore {\text{Desired profit }}\% \cr & = \left( {\frac{x}{5} \times \frac{5}{{6x}} \times 100} \right)\% \cr & = 16\frac{2}{3}\% \cr} $$