Its much easier to use decimals, however you can use "fractions" by simple addition and division. For your example, 1 1/2 = 1+(1/2) although this can also be written 1+1/2 since division takes precedence.
Agree with darkagn.
BUT multiplication - be careful this will also take precedence (BODMAS, PODMAS, BIDMAS, PIDMAS - whatever you want to call it).
So place the term to be multiplied within brackets, otherwise you'll just multiply the integer or the fraction.