The holders of a majority of the voting power of the shares entitled to vote at a meeting are a quorum for the transaction of business, unless a larger or smaller proportion or number is provided in the articles or bylaws. If a quorum is present when a duly called or held meeting is convened, the shareholders present may continue to transact business until adjournment, even though the withdrawal of a number of shareholders originally present leaves less than the proportion or number otherwise required for a quorum.