I repeat my suggestions given in my answer to http://meta.physics.stackexchange.com/questions/7407/generalizing-the-homework-policy/9058#9058Generalizing the homework policy.
Duplicates : It is very difficult to avoid them, and checking is tedious. Even where they are identified before new answers are posted, existing answers may be unsatisfactory, or there may be a subtle difference. Reviving an old question is not easy for a new user (see http://meta.physics.stackexchange.com/questions/8974/Re-asking a Duplicate Question).