Question

Mark (✓) against the correct answer:
On selling 100 pens, a man gains the selling price of 20 pens. The gain per cent is
(a) 20%
(b) 25%
(c) $16\frac{2}{3}\%$
(d) 15%

Answer 1

(b) 25%
​
$$\begin{gathered} \mathrm{Let}\mathrm{Rs}x\mathrm{be}\mathrm{the}\mathrm{SP}\mathrm{of}100\mathrm{pen}s. \\ \mathrm{SP}\mathrm{of}1\mathrm{pen}=\mathrm{Rs}\frac{\mathrm{x}}{100} \\ \mathrm{Profit}\mathrm{on}100\mathrm{pen}s=\mathrm{selling}\mathrm{price}\mathrm{of}20\mathrm{pens} \\ =\frac{20}{100}\times x \\ =\frac{\mathrm{x}}{5} \\ \mathrm{Now},\mathrm{CP}=\mathrm{SP}-\mathrm{Profit} \\ =x-\frac{\mathrm{x}}{5} \\ =\frac{4\mathrm{x}}{5} \\ \therefore \mathrm{Profit}\mathrm{percent}\mathrm{on}100\mathrm{pens}=\frac{\mathrm{profit}}{\mathrm{CP}}\times 100 \\ =\frac{\frac{\mathrm{x}}{5}}{\frac{4\mathrm{x}}{5}}\times 100 \\ =25\% \end{gathered}$$