Mo. Rev. Stat. § 351.325: Board, quorum.

A majority of the full board of directors shall constitute a quorum for the transaction of business unless a greater number is required by the articles of incorporation or the bylaws. The act of the majority of the directors present at a meeting at which a quorum is present shall be the act of the board of directors, unless the act of a greater number is required by the articles of incorporation or the bylaws.