This statistics question has been making the rounds. It is elegant and wonderful for many reasons.
First, let's just say this is a basic, classic, statistics question, with a twist. It forces the reader to pay close attention. I think, in a math classroom, the students who assumed they knew how to answer the question would probably get it wrong because they wouldn't read it entirely or carefully. In a test prep classroom it could easily begin a conversation about test taking strategies, the importance of slowing down, reading every word, double checking work, the list goes on and on.
There's a online "IQ test" that was making the rounds a few years ago. I used to use it in my classroom the day or two before the standardized tests were given. I did it to break some of the tension the students were feeling, to remind them of the test taking strategies we had reviewed in prior weeks, and to underline the importance of reading slowing and carefully. This one statistics question can start the same type of conversion.
There's also a classic "follow all instructions" test out there that I've seen over and over again given to middle school students. I was able to find a copy of it here.
Do you have any questions like this? How do you engage students to focus on some of these skills?