If all you're looking for is the correct answer to be displayed as a fraction, then you can simply pass a string to Compute rather than a real number (which is the way Compute is supposed to be used):

```
Context("Numeric");
$ans = Compute("3/8");
BEGIN_PGML
[`3/8 = `] [__]{$ans}
END_PGML
```

Note that this won't reduce fractions. In that case you will have to do something with Fraction objects.