what the 2000th bet is purchased or sold at, not the new probability is what determines how the question resolves.

A purchase or sale at 45% and question resolves to yes
A purchase or sale at 55% and question resolves to yes
A purchase or sale anywhere between 45% and 55% and question resolves to yes

Once 2,000 or more trades have been reached they will be copied from the "trades" page and pasted in an excel spreadsheet to determine the 2,000th trade.

If 2,000 trades are not reached by the closing date the last trade made will decide how the question resolves.