Hello everybody

I have a small problem...

I have entered 2.5% in A1, 100% in A2 ans 100 in A3.

In A4 I have the following formula: =A3*(1+$A$1)-(A3*$A$1) with the
result 100.
(In fact I calculate an interest on a certain amount and just after I
withdraw the interest)

Now I copy this formular in the next 20 cells beneath A4 and I recieve
the following results:

A5: 100
A6: 100
A7: 99.999999999999900 ????
A8: 99.999999999999900
A9: 99.999999999999900
A10: 99.999999999999900
A11: 99.999999999999900
A12: 99.999999999999900
A13: 99.999999999999900
A14: 99.999999999999800 ????
A15: 99.999999999999800
A16: 99.999999999999800
A17: 99.999999999999800
A18: 99.999999999999800
A19: 99.999999999999800
A20: 99.999999999999800
A21: 99.999999999999700 ????
A20: 99.999999999999700

and so on (this value remains).

Shouldn't the result of this calculation always be exactly "100"?

What do I do wrong? Thank you very much for any help.

best regards, Tobias