Some articles were bought at 6 articles for Rs. 5 and sold at 5 articles for Rs. 6. Gain percent is:

$$\eqalign{ & {\text{Suppose,}}\,{\text{number}}\,{\text{of}}\,{\text{articles}}\,{\text{bought}} \cr & {\text{ = }}\,{\text{L}}{\text{.C}}{\text{.M}}{\text{.}}\,{\text{of}}\,{\text{6}}\,{\text{and}}\,{\text{5 = 30}} \cr & {\text{C}}{\text{.P}}{\text{.}}\,{\text{of}}\,{\text{30}}\,{\text{articles}} \cr & = Rs.\,\left( {\frac{5}{6} \times 30} \right) = Rs.\,25 \cr & {\text{S}}{\text{.P}}{\text{.}}\,{\text{of}}\,{\text{30}}\,{\text{articles}} \cr & = Rs.\,\left( {\frac{6}{5} \times 30} \right) = Rs.\,36 \cr & \therefore {\text{Gain}}\,\% = \left( {\frac{{11}}{{25}} \times 100} \right)\% \, = 44\% \cr} $$