The answer isn't black and white and is going to depend on a few things.
1. Has this question been asked before? If it has and your answer is different to the existing answers, then just answer the existing question. Don't add your answer if you are duplicating existing answers.
2. Has this q&a been repeated ad nauseam on the web? If it has adding it to Islamiqa seems unnecessary and potentially draws traffic away from a potentially better resource.
3. Is the answer common knowledge? If it is don't add just for the sake of adding it to Islamiqa. It just adds more clutter to readers' feeds which they will not appreciate.
If the you pass all of the above go ahead and write a good question and answer.
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