[Zope] float calculation in ZSQL Method??

[Atuc]

hallo,

i have the problem to make a calculation in an ZSQL Method, i would like to 
add the two floats like this. what i get is only a string adding!

i get this if i give the numbers 1 and 100, i would like to get 101

SQL used:
select * from RegionRef
where
ContainerId1 = 'c3b0fef5-4ab7fb9e-4abe43d4-7f149316' AND
RegionRef.positionX >= 1 AND
RegionRef.positionX <= 1100


any ideas if it is possible?

this is my ZSQL Method:

select * from RegionRef
where
ContainerId1 = <dtml-sqlvar ContainerId type=string> AND
RegionRef.positionX >= <dtml-sqlvar Position1 type=float> AND
RegionRef.positionX <= <dtml-sqlvar expr="Position1+Position3" type=float>

thanks
alex