David sold a bicycle at Rs 2100 and made a loss of 25%. At how much price he should sell the bicycle if he wants to make a profit of 15%?

$(\eqalign{
& {\text{As we know that profit% }} = {\text{}}\frac{{Selling\ price - Cost\ Price}}{{cost\ price}} \times 100 \cr
& {\text{Also loss% }} = {\text{}}\frac{{Cost\ price - Selling\ Price}}{{cost\ price}} \times 100 \cr})$


=> Selling Price = Cost Price (1 – Loss %)


David sold the bicycle at Rs 2000 and made a loss of 25%.


Hence cost price = (2100/0.75) = Rs 2800


So the cost price of the bicycle is Rs 2800.


Now the selling price when he makes a profit of 15% = 115% of 2800


= Rs (1.15 × 2800) = Rs 3220


Alternate Method (Short trick):


$(Required\ selling\ price = \frac{{2100}}{{100 - 25}} \times \left( {100 + 15} \right) = \frac{{2100}}{{75}} \times 115 = 3220\ rupees)$