A trader has purchsed pens at the rate of Rs. 42 per dozen. If the profit earned is 14 2/7% what is the selling price?

CP of 1 pen = Rs. 3.50

profit % = $\frac{100}{7}\%$

$profit\%=\left[\frac{profit}{CP}\times 100\right]\%\phantom{\rule{0ex}{0ex}}\Rightarrow \frac{100}{7}=\frac{profit}{7/2}\times 100\phantom{\rule{0ex}{0ex}}\Rightarrow Profit=Re.0.50\phantom{\rule{0ex}{0ex}}Profit=SP-CP\phantom{\rule{0ex}{0ex}}\Rightarrow SP=0.50+3.50=Rs.4.00$

SP of a pen = Rs. 4.00

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