I would say that 1.3 is the simplest form.
If you want it as a simplified fraction, then the answer is 13/10 - in my view this is not simpler than 1.3.
10/13 is the simplest form.
It is already in its simplest form as 4/13
13/45 is already in simplest form.
5/13 is in its simplest form.
65/13 in simplest form is 13/1
3.25 = 13/4 as a fraction in its simplest form
4/52 = 1/13 in simplest form
13/100
it is in simplest form unless you want to write in decimals.....
That would be 13/50 in its simplest form.
-2.65 in simplest form is -2 13/20
2.6 written as a fraction in simplest form is 13/5