Rounding Count for time query

I'm having a problem running the following query: select decode(home_community_name, '9.9', 'Total',home_community_name) as homeCommunityName, round(avg((a.end_time - a.start_time ) * 24 * 3600)) as Count from vleruser.actions a, vleruser.uddi_lookup b where a.home_community_id = b.home_community_id and a.action_type_id in (102) and a.status_code in (0,2,9) and a.start_time >= TO_DATE('2015-05-01 01:00:00', 'YYYY-MM-DD HH24:mi:ss') and a.start_time <= TO_DATE('2015-05-25 23:59:59', 'YYYY-MM-DD HH24:mi:ss') group by home_community_name; I'm getting the following error: ORA-00932: inconsistent datatypes: expected NUMBER got INTERVAL DAY TO SECOND 00932. 00000 - "inconsistent datatypes: expected %s got %s" *Cause: *Action: Error at Line: 1 Column: 140 Not sure how to solve it.