(1) The term "serial bonds" means a bond issue payable in equal annual installments, one installment consisting of one or more bonds becoming due and payable each year.
(2) The amount to be paid and redeemed each year shall be determined by dividing the total amount of the bonds to be issued by the total number of years the issue is to run so that the total amount of principal to be paid each year will be the same.
(3) The amount of installments becoming due and payable the first year or the first and second years may vary from the others to the extent which results from fixing the amounts of each bond of the other installments at $100, $500, or $1,000, as may be determined by the board.