(a) Unless otherwise provided by ordinance, a runoff election shall be held if no candidate receives over 40 percent of the votes cast for the office of
(1) mayor; or
(2) member of the governing body or school board if candidates run for a designated seat.
(b) Unless otherwise provided by ordinance, if candidates for the governing body or school board run at large, a runoff election for a seat shall be held if no candidate receives a number of votes greater than 40 percent of the total votes cast for all candidates divided by the number of seats to be filled.
(c) Unless otherwise provided by ordinance, a runoff election shall be held within three weeks after the date of certification of the election for which a runoff is required, and notice of the runoff election shall be published at least five days before the election date. The runoff election shall be between the two candidates receiving the greatest number of votes for the seat.