Try

 Select mb.blockid
      SUM( DATEDIFF( mi, mb.BEGINTIME, mb.ENDTIME)) AS blocktime, 
      SUM( DATEDIFF( mi, ap.BEGINTIME, ap.ENDTIME)) AS usedtime,
      SUM( DATEDIFF( mi, ap.BEGINTIME, ap.ENDTIME)) /
        SUM( DATEDIFF( mi, mb.BEGINTIME, mb.ENDTIME)) AS used, 
  FROM  meetings mb 
  JOIN  meetings ap ON mb.BLOCKID = ap.BLOCKID 
    AND mb.ISBLOCK = 1 AND ap.BLOCKMEMBER = 1
  GROUP BY mb.blockid

>I have a table called meetings with the following:
>
>

>MEETINGID BEGINTIME           ENDTIME           ISBLOCK  BLOCKID BLOCKMEMBER
>INT          DT                 DT               BIT      INT      BIT
>------------------------------------------------------------------------
>1         12/14/2001 07:00   12/14/2001 12:00     1        1        0
>2         12/14/2001 07:00   12/14/2001 08:00     0        1        1
>3         12/14/2001 08:15   12/14/2001 09:45     0        1        1
>

>
>I need to create a sp that returns the percent of time used for a given blockID.
>In the example above, the first record represents the block itself and the total available for the block (ISBLOCK is the flag). The second and third record represent appts scheduled within the block (Represented by BLOCKMEMBER) and tied to the block by BlockID
>
>In the above case I know that I have 5 hours of which 1.5 hours are used so I want to return .30 as used.
>
>I'm hoping someone can give me a pointer how how to structure the SQL command.
>
>Thanks in advance