To compare two fractions, get their common denominator, which is 60 in this case, and rewrite the fractions in terms of this denominator.
3/5 is 36/60 (i.e., 3*12/60) and 5/12 is 25/60 (i.e., 5*5/60).
Compare numerators: 36 is bigger than 25, so 3/5 is bigger.
Now that wasn't so bad, was it?