fixed type (delta) in ada

[nap@nobody.com (Nap)]

does anyone know why mutiplication between fixed type in ada produce a
big round off error?

type money is delta 0.01 range 0.0..100_000_000.00;
a, b, c : money;

package money_io is new ada.text_io.fixed_io(money);

a := 351.00;
b := 0.20;
c := a * b;

money_io.put(c);

-- the output should be 70.2 but it prints 71.3 instead.
-- this is so frustrating. typecasting (back to float) doesn't help
either. 

Thanks,
Nap