Flash doesn't add numbers right... help!

Hi everybody! Thanks in advance for your help!

Here’s my problem:

sometimes when within an onEnterFrame, when I add var1+=var2 flash doesn’t do it’s Math the right way. It sort of says 2.15+2.45=4.55 I’m using trace() to check on the values and that is exactly what it does.

What’s the explanation for this and how can it be fixed?

Thanks!