calculation error with built-in command CTRL + J?!

[Borde, Andreas]

Hello,

I calculated
(* 12 2.6) with the built in command CTRL + J and got
31.200000000000003

It is the same for
(* 2.6 12)

I am wondering about the tailing numbers after 31.2!

If I calculate (* 2.5 12) then the result is the expected 30.0.

Can someone tell me the reason?  Is there something wrong with
my calcuation?

I am using the official release:

This is GNU Emacs 22.1.1 (i386-mingw-nt5.0.2195)
 of 2007-06-02 on RELEASE

under Win2k.

Thank you and kind regards

Borde, Andreas