select up.university, qd.difficult_level, round(count(qpd.question_id)/count(distinct qpd.device_id),4) as avg_answer_cnt from user_profile up inner join question_practice_detail qpd on up.device_id=qpd.device_id inner join question_detail qd on qpd.question_id=qd.question_id where up.university='山东...