110 ILCS 805/3-9

A majority of full voting membership of the Board shall constitute a quorum. For all meetings of the Board, a quorum of members must be physically present at the location of the meeting. When a vote is taken upon any measure before the Board, a quorum being present, a majority of the members voting on the measure shall determine the outcome thereof. No action of such board shall be invalidated by reason of any vacancies on such board, or by reason of any failure to select any nonvoting student members.