The average daily attendance for the fiscal year of pupils residing in a county of this state and attending a school in an adjoining state under Article 1 (commencing with Section 2000) of Chapter 7 of Part 2 of Division 1 of Title 1 shall be computed by dividing the total number of days of attendance of the pupils in the school by the number of days the school was maintained during that fiscal year, but by not less than 175.