I'm not sure it's true to say that that task requires the exact same reasoning - There are various logically equivalent ways of phrasing the rule such as "No ca

I'm not sure it's true to say that that task requires the exact same reasoning - There are various logically equivalent ways of phrasing the rule such as "No card has a D on one side and a number other than 3 on the other" which make the problem easier. Since the rule "you can't drink alcohol if you're underage" is one people are familiar with, they aren't being asked to make the same logical deduction they do in the letters and numbers question. I'd go further and speculate that they aren't all reading the question carefully - if you replaced the rule by "if someone is over 21 they are drinking beer", how many people would get it wrong?