You can do computations on fractions in Z3
FRACTION("1 1/2").add(FRACTION("1 1/2"));
FRACTION("1 1/3").subtract(FRACTION("1 1/2"));
FRACTION("1 1/3").multiply(FRACTION("2 5/3"));
FRACTION("1 1/3").divide(FRACTION("2 5/3"));
z^3 uses the following notation for fractions. 2%%3 for 2/3 (1.2%%3) for 1 2/3 etc.
5%%5<+>4%%5
gives 1.8
To convert the results to fractions, use %% operator at the end of the expression.
(5%%5<+>4%%5)%%
gives
1 4/5
Note fraction additions etc. uses the Unit Conversion operators such as <+>, <->, etc. Hence it is also possibly to convert to meters etc.
(4%%5)<+>((1%%5)<>m)
gives 1m.
((4%%5)<+>((1.3%%5)<>m))%%
gives
2 2/5m
((4%%5)<+>((1.3%%5)<>m))%%;
2 1250000000000001/3125000000000000
2.4%%;
((4%%5)<>m)<+>((1.3%%5)<>m)
2.4000000000000004m
(4%%5)<+>((1.3%%5)<>m)
2.4000000000000004m
((34%%5)<>m)<+>((1.3%%5)<>m)
8.4m
((3.4%%5)<>m)<+>((1.3%%5)<>m)
5.4m
(((3.4%%5)<>m)<+>((1.3%%5)<>m))%%
5 1250000000000001/3125000000000000
etc.