If loss is $$\frac{1}{3}$$ of S.P., the loss percentage is -

$$\eqalign{ & {\text{Let S}}{\text{.P}}{\text{.}} = {\text{Rs}}.\,x \cr & {\text{Then,}} \cr & {\text{Loss}} = {\text{Rs}}.\frac{x}{3} \cr & {\text{C}}{\text{.P}}{\text{.}} = {\text{Rs}}.\left( {x + \frac{x}{3}} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\, = {\text{Rs}}.\frac{{4x}}{3} \cr & \therefore {\text{Loss }}\% \cr & = \left( {\frac{x}{3} \times \frac{3}{{4x}} \times 100} \right)\% \cr & = 25\% \cr} $$