One can do fractional math by recording the numerator and denominator separately. The problem is that the set of rational numbers is not closed over some math operations; So you have to avoid those operations. So, you really don't gain that much for all of the extra storage.

One can do fixed decimal math by remembering the location of the decimal place. I've worked on many systems that record every thing as pennies.

Of course there is a problem with every mathematical system we used because it is impossible to create a math system that is complete.