select
     event as "TOP 5 Timed Events",
     round(cnt / (last_value(mxsid)
                 OVER (  ORDER BY mxsid
                   ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
                 -
               first_value(mnsid)
                  OVER ( ORDER BY mnsid
                ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING ) ),2)  asl
  from (
      select  substr(decode(session_state,
                     'ON CPU','CPU',event),0,25) event ,
               count(decode(session_state,
                     'ON CPU','CPU',event)) cnt,
               max(SAMPLE_ID) mxsid,
               min(sample_id) mnsid
       from
           v$active_session_history
       where
          SAMPLE_TIME > sysdate - (5/(24*60)) and
          SESSION_TYPE = 'FOREGROUND'
       group by  decode(session_state,'ON CPU','CPU',event)
       order by  count(decode(session_state, 'ON CPU','CPU',event)) desc
) where rownum < 6
order by asl desc
/