Calculate the average duration of absense of female students.
average duration = DIVIDE(SUM(month), COUNT(longest_absence_from_school.name which are NOT in male.name)); female students refers to longest_absence_from_school.name who are NOT in male.name;
SELECT AVG(T2.month) FROM person AS T1 INNER JOIN longest_absense_from_school AS T2 ON T1.name = T2.name LEFT JOIN male AS T3 ON T1.name = T3.name WHERE T3.name IS NULL