If a saree is sold for Rs. 2880, the seller will incur a loss of 10%. At what price should he sell it to gain a profit of 20%?

Given that the saree is sold for Rs. 2880 with a 10% loss.

When there is a 10% loss, the selling price is 90% of the cost price.

$\text{Selling Price} = 90\% \times \text{Cost Price}$

$2880 = \frac{90}{100} \times \text{Cost Price}$

$2880 = 0.9 \times \text{Cost Price}$

$\text{Cost Price} = \frac{2880}{0.9}$

$\text{Cost Price} = 3200$

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To gain a profit of 20%, the new selling price must be 120% of the cost price.

$\text{New Selling Price} = \text{Cost Price} + 20\% \times \text{Cost Price}$

$\text{New Selling Price} = 3200 + \frac{20}{100} \times 3200$

$\text{New Selling Price} = 3200 + 0.2 \times 3200$

$\text{New Selling Price} = 3200 + 640$

$\text{New Selling Price} = 3840$

Therefore, the saree should be sold for Rs. 3840 to gain a profit of 20%.