Why Restate HW Problems?

A student asks:
"In class, you said you would like us to write out both the questions and the answers. I'm a bit confused as to what extent. Would you like us to write out the entire text of the question and the sentences to be rewritten?

"I ask, because I have been writing out the questions in their entirety, and, in some cases, it seems superfluous and would actually make the homework messier and more difficult to grade."

Prof. Rapaport answers:
Suppose I get a HW from a student with the answer "42". How do I know what the question is? It could be "What is 6 * 7?", or it could be "What is the answer to the ultimate question of life, the universe, and everything?".

The rule of thumb you can use is this:

Someone reading your HW should be able to figure out what problem you are answering, as well as what your answer is.

If that means that you can get away with copying less than the full problem, that's OK.