select u.university , qd.difficult_level, round(count(u.answer_cnt) / count(distinct u.device_id),4 ) avg_answer_cnt from user_profile as u, question_practice_detail as qpd ,question_detail as qd where qpd.device_id = u.device_id and qpd.question_id = qd.question_id group by u.university , qd.di...