I sold two watches for Rs. 300 each, one at loss of 20% and other at the profit of 20%. What is the percentage of loss (-) or profit (+) that resulted from the transaction?

Answer: Option D

In such cases, always loss occurs. It can be calculated by this formula,
$$=\frac{{\left(\text{loss or gain percentage}\right)}^2}{100}=4$$
That is 4% of loss

Graphic Change method
100 == 20%(loss) ⇒ 120 == 20%(gain) ⇒ 96
% Loss = 4%