I've taken the Wonderlic before. A few of the questions were tricky, but these samples are the sort of thing I remember. You have to read very carefully to make sure you are answering the question that was asked. As others have stated, the time is the big thing. Takes some self discipline to read carefully when you need to average about 4 questions a minute. If you get behind, I could see where it would get really intense. One of the techniques is knowing when to "sacrifice" a question -- i.e. yes, I may be able to answer this math problem, but it'll take me about a minute to do the calculation, better to just take my best guess and work on other questions I can do faster or perhaps return to it.
That said, it is a little scary that high school graduates with at least several semesters of college work, if not an actual degree, are scoring in the single digits or low teens out of 50 questions. My bet would be that as a group, offensive linemen score higher than anyone.