A lot of comments complaining that many of the problems don't have definitive answers, e.g. #12 (tides) and #13 (bookworms). I think the point for some problem

A lot of comments complaining that many of the problems don't have definitive answers, e.g. #12 (tides) and #13 (bookworms). I think the point for some problems is not finding the answer so much as developing logical, analytic and critical thinking skills; to learn the value of looking at a problem from different perspectives and the necessity to sometimes think outside of the box; and to be able to find the holes and ambiguities -- sometime to even reject the question outright.