What is the average number of crimes in a neighborhood in Central Chicago?
Central Chicago refers to side = 'Central'; average number = divide(count(report_no), count(community_area_no))
SELECT CAST(COUNT(T1.report_no) AS REAL) / COUNT(T2.community_area_no) FROM Crime AS T1 INNER JOIN Community_Area AS T2 ON T1.community_area_no = T2.community_area_no WHERE T2.side = 'Central'