Let's say that a question is posted, asking how to find $$\sum_{k=1}^n2k^2.$$ It is proposed that the question be closed as a duplicate of a much older one, asking how to find $$\sum_{k=1}^nk^2,$$ but before the closure is complete, a user posts identical answers on both questions explaining how to find something like $$\sum_{k=a}^nbk^2.$$ My question is, should this be allowed, or should the user be asked to delete one of the copies? Something similar to the above (though with different math) occurred recently, and I'd just like to get some community input. I am strongly in favor of deleting the copy on the closed question.
Martin Sleziak has found some relevant meta.SO links and posted them in the comments, and I will include them in my post below. Of course, we have no requirement to follow the SO community's policies.
Is it acceptable to add a duplicate answer to several questions?
User posting exact duplicate answers to multiple questions
What should I do with automatic flags about identical posts?
Can we hash answers and check for duplicates (upon submission)?