No.
No.
Only if the fraction is improper (greater than one).
rename 8/1 as a whole number
If you can do it without, go ahead. But it helps to get the correct answer, since three is larger than one. If you re-name 4 and 1/4 to 3 and 5/4, it's easier to subtract 3/4 from it.
When adding or subtracting fractions with different denominators their lowest common denominator must be found first by using the LCM of their denominators
It is still a subtraction problem.
Probably not, but it depends on what you mean by "3th".
prime numbers, yes
When doing sums with mixed numbers, it is often easier to convert the mixed numbers to improper fractions, do the sum and convert any resulting improper fraction back to a mixed number. This is especially true of division, but with subtraction, if the fraction part of the second mixed number is larger than the fraction part of the first mixed number (subtracting the second from the first), this will result in requiring borrowing from the whole number of the first mixed number. Using improper fractions avoids this complication and makes all sums easier.
You rename a directory the same way you rename a file. Use the 'mv' command to rename it.
Because you cannot subtract 3/4 from 1/4.
No, you would have to make the code.