What is the average number of dishes per menu page of menu ID12882?
average number of dishes per menu = DIVIDE(COUNT(dish_id), COUNT(page_count));
SELECT CAST(COUNT(dish_id) AS REAL) / COUNT(T3.page_count) FROM MenuItem AS T1 INNER JOIN MenuPage AS T2 ON T1.menu_page_id = T2.id INNER JOIN Menu AS T3 ON T2.menu_id = T3.id WHERE T2.menu_id = 12882