SDCL § 9-7-7: Quorum--Majority required for action.

A majority of the members of the board of trustees constitutes a quorum, but an act of the board is not effective unless assented to by a majority of the members. Unless a vacancy exists due to removal, resignation, death, or by operation of law, the quorum consists of the majority of all the trustees qualified to serve as trustees by election or appointment pursuant to chapter 9-13.