select
 a.tot as tot_topten, round(a.tot / a.cnt,1) as avg_topten
from (
  select count(*) as cnt, sum(score) as tot from (
    select
     @rnum:=@rnum+1 as rownum, a.*
    from (select @rnum:=0) r, reportcard a where sdate between '2013-03-01' and '2013-03-19'
    order by a.score desc
  ) a
  where a.rownum <= (select round(count(*)*0.3) from reportcard where sdate between '2013-03-01' and '2013-03-19')
  order by a.score desc
) a