>>Start with the select first - verify that select produces right data. Then turn SELECT into update.
>sorry Noomi: i can not under stand

Try

select Ex.*, Hv.*, 
ceiling((Hv.Perc+0.9)/10) as FinalValue from Exam Ex inner join Hwsv Hv ;
on Ex.Code = Hv.Code

If this select statement works correctly, then the original UPDATE statement should have worked correctly too.
If not, post what is wrong in this select statement.