I sold two watches for Rs. 300 each, one at the loss of 10% and the other at the profit of 10%. What is the percentage of loss(-) or profit(+) that resulted from the transaction?

Selling price of first watch = 300
Profit = 10%
cost price = $$\frac{300}{1.1}$$
Selling price of second watch = 300
Loss = 10%
cost price = $$\frac{300}{0.9}$$

Total selling price of transaction= 600
Total cost price of transaction = $$300(\frac{10}{11} + \frac{10}{9}) = 600 (\frac{100}{99})$$
Loss = $$600 (\frac{100}{99} - 1)$$
%loss = $$(600 (\frac{100}{99} - 1)) \div (600(\frac{100}{99})) \times 100 = 1$$