By selling two items at the same price, a person gains 20% on one item and loses 20% on the other. Then over all  

Concept:

 Net loss = \(\left( \frac{\text{Common gain/loss percentage}}{10} \right)^2 \%\)

Explanation:

If a person gains \(x\% \) on one item and loses \(x\% \) on another item, the net result will always be a loss. 

Net loss = \(\left( \frac{\text{Common gain/loss percentage}}{10} \right)^2 \%\)

Here, the common percentage is 20%, so the net loss is

\(\text{Net loss} = \left( \frac{20}{10} \right)^2 = 2^2 = 4\%\)

Therefore, the person incurs a net loss of 4%.

Thus, the correct option is Option 3).