In any school district or community college district situated wholly or partly within a city containing a population of over 1,900,000 according to the 1950 federal census, the governing board shall be composed of seven members holding office numbers 1, 2, 3, 4, 5, 6, and 7, and shall be elected at large at the same time and in the same manner as the members of the city council of said city, and shall serve for a term of four years. The four members of such board whose terms of office expire July 1, 1947, shall be considered as holding office numbers 1, 3, 5, and 7 (such members within 15 days after the effective date of Chapter 725 of the Statutes of 1945 to determine by lot at a regular board meeting the number of the office each holds), and the remaining offices shall be known as office numbers 2, 4, and 6 (to be allocated by lot in the same manner as hereinbefore provided for office numbers 1, 3, 5, and 7). All such members’ terms shall commence on the first day of April next succeeding their election.