How clever are you?

Take this simple Observer quiz to find out your overall intelligence level

Although a full IQ test takes an hour or more and costs hundreds of pounds, performance on this one simple test is highly predictive of your overall intelligence.

Look at the four cards above. We know for a fact that each card has a letter on one side and a number on the other. Truthful Terry says: 'Every card that has a D on one side has a 3 on the other.' What is the fewest number of cards you need to turn over to find out whether Truthful Terry is actually telling the truth? And which ones? The answer is shown at the bottom of the page.