select sum(qty*unitpri) wrong result

[wang shuming]

Hi,
 table a1

qty int(10) , unitpri foat(10,2)
350            19.80
  ...
350     19.80    (total 48 lines)

select sum(qty*unitpri)  from a1
332639.99  ,it should return  332640.00

mysql version 4.1.19

Best regards!

Shuming Wang