all of my best answers for these questions ... would take way more than 250 words to explain.

Not true, especially if you just say what they are, as opposed to truly explaining them. For example, you don't say "Newcomblike problems, which are hypothetical situations where... (etc)", you say, "Newcomblike problems, a notorious class of philosophical dilemmas which I believe have real-world implications". Do this in a first draft and you will actually have room left to expand on the description in a second draft.