I have seen some very similar questions to the site, and have an answer that I think will help future readers. Is it OK to post the exact same answer to all of these questions?
Identical questions: no
If questions are similar enough that the same answer fits them both, they should be marked duplicates. Answering questions that are duplicates could just give users an incentive to ask questions without verifying the question was already asked; in the long run, this is harmful to the site.
If questions are different enough not to be duplicates, the answers should be tailored to the question, not copy-pasted from a question to another.
Similar questions: sometimes
Sometimes questions are different enough that cannot be considered duplicates. In this case, answering both questions doesn't cause any harm. Even in this case, it's rare that the same answer can be used for more than one question, but it could be the case if the answer doesn't give a detailed explanation. It is always better to tailor the answer for the question.