Try this
if object_id('tempdb..#temp') is not null
drop table #temp
create table #temp
(
AverageMark decimal(10,2),
Position int
)
insert into #temp(AverageMark)values(97)
insert into #temp(AverageMark)values(96)
insert into #temp(AverageMark)values(25)
insert into #temp(AverageMark)values(36)
insert into #temp(AverageMark)values(78.25)
insert into #temp(AverageMark)values(96)
select AverageMark,
rank() over(order by AverageMark desc) as Position
from #temp
order by AverageMark desc
select AverageMark,
(select count(*) from #temp where AverageMark > a.AverageMark) + 1 as Position
from #temp a
order by AverageMark desc