321/1000 is the simplest form.
3.21 is, itself, a fraction. It is a fraction in decimal form rather than in the form of a ratio. However, that does not stop it being a fraction. Its equivalent, in rational form, is 321/100. It is in its simplest form.
3.21 = 321/100 or 321/100
3.21 = 321/100. That is the number in the form of the simplest fraction though I would not say that is a simpler form than 3.21!
It is 1 to 5 as a ratio in its simplest form
That is the simplest form.
321/107 = 3 ... it can't any simpler than that.
The ratio 27 to 78 in its simplest form is 9 to 26
The ratio of 338 to 382 in its simplest form is 169 to 191