The secretary of state must certify to the county auditor of each county on or before the first day of April preceding a general election the number of representatives in the legislature said county will be entitled to elect at the following election. When any new county has been created, subsequent to the last general election for governor, the total vote cast for governor in the territory included in such new county and in the territory remaining in any county or counties from which said new county has been created shall be estimated by the secretary of state as nearly as possible from the election returns and the legislative apportionment figured thereon.