To make a quick contra profit, traders can take advantage of the last 30 minutes of trading hours

During this last half an hour, if certain stock suddenly becomes active with a surge in price, chances are it will gap up when the market opens the next day. It will be more so if it closes at day high. Hence, go long before the market closes today.

On the other hand, if high volume is coupled with a plunge in price, it will likely gap down when the market opens the next day. It will be more so if it closed at day low. Hence, go short before the market closes today.