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) $16 \frac{2}{2} \%$
(d) 15%
Solution:
(b) 25%
Let Rs $x$ be the SP of 100 pen $s$.
SP of 1 pen $=$ Rs $\frac{x}{100}$
Profit on 100 pen $s=$ selling price of 20 pens
$=\frac{20}{100} \times x$
$=\frac{x}{5}$
Now, CP $=$ SP $-$ Profit
$=x-\frac{\mathrm{x}}{5}$
$=\frac{4 \mathrm{x}}{5}$
$\therefore$ Profit percent on 100 pens $=\frac{\text { profit }}{\mathrm{CP}} \times 100$
$=\frac{\frac{x}{5}}{\frac{4 \mathrm{x}}{5}} \times 100$
$=25 \%$