You don't have to know the answer to any of these to get hired...
Funny thing is, a friend of mine was interviewing someone over the phone and asked me for brain teasers, I googled and gave him 'how many golf balls does it take to fill a emptied out 747'. LOL.
Neh, the answer have nothing to do with how good the candidate is. His interview was over before that question was asked. The interviewer is just trying to f' around w/ the intervewee. Just relax, stay composed, and say anything that makes any remote sense and you'd have considered passing these brain teasers.
I work for one of the largest software companies in Seattle. And I can tell you nowadays a lot of companies don't ask these types of questions any more. They tend to ask more practical/job-related person as they are more focused on the quality of the applicant overall instead of the just the intelligence.
As someone mentioned above, the goal may not be to get an exact answer. One question I was asked was "design an alarm clock for a blind person". The goal is to know about how customer focused you are, and what your thought process would be.