Final answer:
The shopkeeper's gain percent during the sale season is -10%.
Step-by-step explanation:
To find the gain percent during the sale season, we need to first calculate the selling price after the discount is applied.
Given that the shopkeeper sells the umbrella for Rs. 300, and gains 20%, we can calculate the cost price as follows:
Cost price = Selling price / (1 + Gain percent)
Cost price = 300 / (1 + 20/100) = 300 / 1.2 = Rs. 250
Now, to find the selling price after the 10% discount is applied, we can calculate it as follows:
Selling price after discount = Cost price - (Discount percent * Cost price)
Selling price after discount = 250 - (10/100 * 250) = Rs. 225
To calculate the gain percent during the sale season, we can use the formula:
Gain percent during sale season = ((Selling price after discount - Cost price) / Cost price) * 100
Gain percent during sale season = ((225 - 250) / 250) * 100 = (-25/250) * 100 = -10%
Therefore, the shopkeeper's gain percent during the sale season is -10%.