Any two members of the board shall constitute a quorum for the transaction of any business or the rendering of any decision required by this chapter to be made by all of the members. (Ga. L. 1920, p. 167, § 53; Ga. L. 1925, p. 282, § 4; Code 1933, § 114-703; Ga. L. 1973, p. 232, § 7.)