If the cost price of 18 articles is equal to the selling price of 16 articles, the gain or loss is = ?

According to the question,
18 Cost Price = 16 Selling Price
$$\eqalign{ & \frac{{{\text{CP}}}}{{{\text{SP}}}} = \left. {\frac{{16}}{{18}} = \frac{8}{9}} \right\}{\text{1 unit profit}} \cr & {\text{Profit}}\% = \frac{1}{8} \times 100 \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 12\frac{1}{2}\% {\text{ gain}} \cr} $$