Mo. Rev. Stat. § 355.401: Quorum and voting.

1. Except as otherwise provided in this chapter, the articles or bylaws, a quorum of a board of directors consists of a majority of the directors in office immediately before a meeting begins. In no event may the articles or bylaws authorize a quorum of fewer than the greater of one-third of the number of directors in office or two directors.

2. If a quorum is present when a vote is taken, the affirmative vote of a majority of directors present is the act of the board unless this chapter, the articles or bylaws require the vote of a greater number of directors.