The board of adjustment shall consist of five, seven, or nine members as determined by the council. Members of a five-member board shall be appointed for a term of five years, excepting that when the board shall first be created one member shall be appointed for a term of five years, one for a term of four years, one for a term of three years, one for a term of two years, and one for a term of one year. Members of a seven-member board shall be appointed for a term of five years, except when the board shall first be created two members shall be appointed for a term of five years, two members for a term of four years, one for a term of three years, one for a term of two years, and one for a one-year term. Members of a nine-member board shall be appointed for a term of five years, except when the board shall first be created three members shall be appointed for a term of five years, two members for a term of four years, two for a term of three years, one for a term of two years, and one for a one-year term. A five-member board shall not carry out its business without having three members present, a seven-member board shall not carry out its business without having four members present, and a nine-member board shall not carry out its business without having five members present. A majority of the members of the board of adjustment shall be persons representing the public at large and shall not be involved in the business of purchasing or selling real estate. Members shall be removable for cause by the appointing authority upon written charges and after public hearing. Vacancies shall be filled for the unexpired term of any member whose term becomes vacant.