Going by the rules of the grammar, we can clearly see that the precedence of / is more than that of -(minus).
So, any string of the form like (id/id) here parenthesis are redundant because even if we don't use them, our result won't change.
Second string is id-(id/id). Here if we draw parse tree for expression id-id/id, then we come to realize that since / appears at a lower level than - so it will be evaluated first. So, here also we don't need parenthesis for /.
As you can see in the above parse trees, the problem comes when we allow only division inside the parenthesis.
So, we modify our grammar as
E->E-T | T
T->T/F | F
F->id | (E-T).
Now, in this grammar, I only allow minus to appear inside parenthesis in case I want - to be evaluated first rather than / as for expression id/(id-id) which is possible to generate via this grammar.