This question already has an answer here:
So what is your policy for the quesions-puzzles, where the author knows the answer and post them for others to have a pleasure for the puzzle?
Following the discussions and simplicity of questions itself I practically sure that following questions are good examples:
Why I am asking:
1. According to: Posting a challenge, and answering it yourself it has sense to ask question and answer it. But those examples doesn't have self answers, so the following link doesn't answer whether those questions should be on site.
2. When I post a puzzle and do not give it an answer (in spoiler tag) in the question itself, there are downvotes because people believe the question can be answered objectively. Sometimes correctly, but when they are not correct It is impossible to prove without answer.
3. When I post a puzzle and DO give it an answer (in spoiler tag) I am questioned what answer do I expect from other people to such a question? This is a reasonable question.
So I would like to make it clear:
1. Can users ask questions, which asks for a solution for a puzzle, they know the solution to?
2. If they can must they add the solution somewhere?
2.1. If they must where should it be? In the question itself (in spoiler tag)? As an usual answer to their own question? As an comment to the question?
3. Should they do something move special about such a questions? (for example, add a specific tag, or say "I know the solution").
The "possible duplicate" Posting a challenge, and answering it yourself answers on the very first question (as "yes"?), but not on the rest 3.