What is the average gpa of Ogdon Zywicki's research assistants?
research assistant refers to the student who serves for research where the abbreviation is RA; prof_id refers to professor’s ID; GPA is an abbreviated name of Grade Point Average where average = AVG(gpa);
SELECT SUM(T3.gpa) / COUNT(T1.student_id) FROM RA AS T1 INNER JOIN prof AS T2 ON T1.prof_id = T2.prof_id INNER JOIN student AS T3 ON T1.student_id = T3.student_id WHERE T2.first_name = 'Ogdon' AND T2.last_name = 'Zywicki'