We used to have a tradition of closing problems that showed too little effort as "unclear what you are asking." The rationale was that we didn't want to answer questions that are "just little puzzles designed to make you learn a concept," because (a) such questions and answers are rarely useful to anyone other than the OP (because they aren't part of any real problem, they are just a little puzzle designed to make you learn) and (b) if we answer the question then the questions isn't even useful to the OP, because then the OP doesn't get the practice thinking it through for themselves.
Instead we would put a comment something like
What have you tried? Where did you get stuck? We want to help you with your specific problems, not just do your work. However, as it is we don't know what this problem is and thus how to help.
(from the link that @David Richerby posted.)
This is the justification for closing as "unclear what you are asking." It is unclear to us what the OP's real missing knowledge is, so we can't provide an answer that will help the OP or future visitors.
Stack exchange has long had a much better mechanism for dealing with problems of exactly this type. It's the downvote. If you hover over the question downvote button you will see that the tooltip says:
This question does not show any research effort; it is unclear or not useful.
@Gilles recent answer to another meta question:
Should we have a close reason "shows too little effort"?
And he links to a very detailed answer from @shog9 on meta.se that weighs many different pros and cons: Should Stack Overflow (and Stack Exchange in general) be awarding "A"s for Effort?
@shog9's last paragraph really drove the point home for me:
During all of the recent discussions surrounding the close queue backlog, something's been bothering me... A pretty big chunk of the backlog is taken up by questions flagged or voted on using this "minimal understanding" reason. That's not surprising in the least - but it's a horribly inefficient way of dealing with these questions. It takes 5 voters to close a question, and because some amount of subject knowledge is required to properly evaluate them finding the right voters is extra-difficult. Meanwhile, folks who interpret the reason as "no effort shown" are pushing more and more questions into the queue every day...
...If they just down-voted the questions, a privilege available to nearly everyone flagging them, they'd drop out of sight a lot faster.
As shocking as the notion that someone might get their work done for free is, that's not a particularly compelling reason to put a lot of effort into closing a question. And if we factor out the downvoting guidance ("This question does not show any research effort; it is unclear or not useful") from our close reasons, they could become considerably more straightforward.
I was already uncomfortable with our habit of closing as "unclear what you are asking", but ever since that answer by @Gilles I've been actually voting "Leave Open" on most of these. (It's actually even more of a pain because you can't downvote from the review queue. If I think the question really deserves a downvote instead of a close-vote I have to open it in another tab.)