FROM NEW SCIENTIST: FOOLED AGAIN

A few little words is all it takes to turn your rational brain to jelly

"Only one of the following statements about a particular hand of cards is true:

There is a king in the hand, or an ace, or both.

There is a queen in the hand, or an ace, or both.

There is a jack in the hand, or a ten, or both.

Is it possible that there is an ace in the hand?

On first examination the answer seems obvious: yes. But ask a formally programmed computer the same question and it will tell you the opposite. If there is an ace, then the first two statements are true. But the puzzle explicitly states that only one statement is true. So an ace is not possible.

Johnson-Laird tested Princeton University students with this problem, and 99 per cent of them got it wrong."