The famous Wason Selection Task runs like this: You are to imagine four cards, each with a number on one side and a letter on the other side. Of two cards, you see only the letter side and you don't know what's on the number side. Of the other two cards, you see only the number side and don't know what's on the letter side. Imagine the four cards laid out as follows:
Here's the question: What card or cards do you need to turn over to test the rule "If there is a K on one side there is a 2 on the other", to see if it is violated? The large majority of undergraduates (and of almost every group tested) gets this question wrong. One common answer: the K and the 2. The correct answer is the K and the 7.