A majority of the public utilities commissioners constitutes a quorum for the transaction of any business, for the performance of any duty, or for the exercise of any power of the public utilities commission. No vacancy in the commission shall impair the right of the remaining commissioners to exercise all powers of the commission. The act of a majority of the commission, when in session as a board, is the act of the commission. Any investigation, inquiry, or hearing which the commission has power to undertake or to hold may be undertaken or held by or before any commissioner designated for such purpose by the commission, and every finding, order, or decision made by a commissioner so designated, pursuant to such investigation, inquiry, or hearing, and approved and confirmed by the commission and ordered filed in its office, is the finding, order, or decision of the commission.