Ambiguous grammar? Could the grammar be parsed by SLR parser?
Your grammar indeed is ambiguous as it currently is, but not because the follow sets of two nonterminals have common elements. The ambiguity I see is that both re2 -> re1 -> expr -> term -> factor -> num -> ε and re2 -> re1 -> expr -> term -> factor -> id -> ε derive the empty word. If you require that num and id are both nonempty, then your grammar is SLR(1) (unless you do weird things to make num and id nonempty).

As an example where your 'follow test' does not work is the following:

S -&gt; A c
S -&gt; B c
A -&gt; a
B -&gt; b


The follow sets of A and B both contain c, but the grammar is SLR(1).

Unfortunately, the only three options I know to test whether a grammar is SLR(1) all have downsides: generating the table and doing the polynomial time test both take quite some time for an exam, and the third method, visual inspection of the grammar, is not very accurate. Finally, 'quickly' writing down the LR(0) automaton (by omitting the items in the states of the automaton) is possible but requires a lot of practice and is still somewhat inaccurate.