The sum is exactly and unequivocally 1.8
48 and 18 are both integers and so is their sum. You do not need any fractions.
The sum of a fraction? Well, to find the sum of the fraction all you do is divide both top and bottom numbers.
7/12 is another.
1/2 1/6 1/6
Add it
The sum of 16 and 18 is 34.
The sum of -18 and 39 is 21.
A mixed fraction.
20, is the sum of 18 and 2.
1-a, which may or may not be a fraction.
It is a mixed fraction.
1/2 + 1/3 +1/12 + 1/18 + 1/36