Going back to my DA25 question:
That is actually from this weeks
New Scientist magazine.
It is the
Wason Card Selection Task and is designed to prove that people will almost always try to prove something is true even when it is easier to prove it false.
Here is what they say about it:
"Typically, 75% of people pick D and 5, reasoning that if these cards have a 5 and a D respectively on their flip sides, this confirms the rule. But look again. Although you are required to prove that if there is a D on one side, there is a 5 on the other, the statement says nothing about what letters might be on the reverse side of a 5. So the 5 card is irrelevant.
Instead of trying to confirm the theory, the way to test it is to try to disprove it. The correct answer is D (if the reverse isn't 5, the statement is false) and 2 (if there's a D on the other side, the statement is false)."