Failure of the licensee to appear at the hearing, after having been notified, may be deemed an admission by him of the act or omission charged in the notice, and in the event of such failure to appear at the hearing, the board of supervisors may revoke the license and permit without further evidence than that which served as the basis for the notice to the licensee. After the hearing is concluded, the board shall, within twenty (20) days, render its decision revoking such license and permit or dismissing the complaint, with a brief statement of its reasons therefor. (Prior gen. code 3-74.5)