What is the average number of reckless homicides that happened in a district?
"RECKLESS HOMICIDE" is the secondary_description; average = Divide (Count(report_no), Count(district_name))
SELECT CAST(COUNT(T2.report_no) AS REAL) / COUNT(DISTINCT T1.district_name) FROM District AS T1 INNER JOIN Crime AS T2 ON T2.district_no = T1.district_no INNER JOIN IUCR AS T3 ON T3.iucr_no = T2.iucr_no WHERE T3.secondary_description = 'RECKLESS HOMICIDE'