A vendor bought toffees at 6 for a rupee. How many for a rupee must he sell to gain 20%?

$$\eqalign{ & {\text{C}}{\text{.P}}{\text{.}}\,{\text{of}}\,{\text{6}}\,{\text{toffees}}\,{\text{ = }}\,Rs.\,1 \cr & {\text{S}}{\text{.P}}{\text{.}}\,{\text{of}}\,{\text{6}}\,{\text{toffees}} \cr & = 120\% \,{\text{of}}\,Rs.\,1 = Rs.\,\frac{6}{5} \cr & {\text{For}}\,Rs.\,\frac{6}{5},{\text{toffees}}\,{\text{sold}} = 6. \cr & {\text{For}}\,Rs.\,1,{\text{toffees}}\,{\text{sold}} = {6 \times \frac{5}{6}} = 5 \cr} $$