NIFT UG 2019 Question Paper with solutions

Let the selling price of each notebook be $\mathit{₹}1$.
Then, selling price of 12 notebooks $=\mathit{₹}12$
Profit = Selling price of 4 notebooks $=\mathit{₹}4$
Cost price $=$ Selling price $-$ Profit $=12-4=\mathit{₹}8$
Profit percentage $=\frac{4}{8}\times 100=50\%$