TSQL return value out of range

[fahedksa]

Declare @fromitem varchar(15), @toitem varchar(15)
set @fromitem=10
set @toitem=60
select categoryid,categoryno ,@fromitem , @toitem from category
where categoryno>=10 and categoryno<=60

thes must return categoryno between 10 and 60
but it return 1 and 2 and 3 and........
Why?

Categoryno varchar(15) becuase there is many items contains letters.
Help Please