select u.university, qd.difficult_level, round(count(qpd.question_id)/count(distinct qpd.device_id),4) as avg_answer_cnt from user_profile u join question_practice_detail qpd on u.device_id=qpd.device_id join question_detail qd on qpd.question_id=qd.question_id group by u.university,qd.difficult_lev...