In general we don't want repeat questions, so as DT said post a comment or answer with a link to the older question. Then hide the newer one later.
This applies no matter how long ago the question was asked, as long as the answer is still correct and relevant. Which it will be in most cases.
The exception is if the older question is now out of date or the answers are wrong (this will probably happen with some of the B&W questions). In this case it's better to hide the old question, then the correct answers will be in the new question.