Well to me it seems like a lot of questions in the real world are formed like this. I.e. if you are asked to find how many customers will buy a book of your website you make some reasonable assumptions like: The world will not come to an end tomorrow You don't ask a person what should be defined as a book or what should be defined as a buy etc. What I mean is that it is good to have the ability to research the common case. And imagine the question about balls was a real problem that your company faced, I don't think you would ask your colleagues all the questions that you pointed out.