How about this one, which is a classic in study of critical reasoning? What's answer & more importantly what percent of general public get it right? Why don't 100% get the correct answer? How do self-described "tea party" membes do (whatever happened to those guys?) Answers anon . . . .
Answer: 1 & 2--those being the two cards that could contain information falsifying the proposition.
15%--the fraction of the general popultion that can answer this problem correctly
This problem, the Wason Selection Task, is a classic in cognitive science