Average Active Sessions

How to find the average active sessions between 2 dates.

  SELECT rollup_timestamp,
         average,
         minimum,
         maximum
    FROM mgmt$metric_daily
   WHERE     target_name = 'TRCOPDOV'
         AND metric_label = 'Throughput'
         AND column_label = 'Average Active Sessions'
         AND rollup_timestamp BETWEEN TO_DATE ('01/11/2015', 'dd/mm/yyyy')
                                  AND TO_DATE ('01/12/2015', 'dd/mm/yyyy')
ORDER BY 1;