This puzzle seems pretty damn simple on the face of it but it’s actually got a lot of people scratching their heads…
Apparently even Harvard students have struggled with it, according to psychologist Daniel Kahneman’s book Thinking Fast and Slow.
Kahneman claims that more than half of students at leading universities actually get it wrong and a whopping 80 per cent of students at other institutions are left bamboozled by the devious question.
So, have a go at it for yourselves… You buy a bat and a ball for £1.10. The bat costs exactly one pound more than the ball.
Simple, you may be thinking. But before you bask in superior smugness let’s let Mr Kahneman himself explain the answer:
A number came to your mind. The number, of course, is 10: 10p. The distinctive mark of this easy puzzle is that it evokes an answer that is intuitive, appealing, and wrong.
Do the math, and you will see. If the ball costs 10p, then the total cost will be £1.20 (10p for the ball and £1.10 for the bat), not £1.10.
The correct answer is 5p. It is safe to assume that the intuitive answer also came to the mind of those who ended up with the correct number – they somehow managed to resist the intuition…
According to Kahneman, many people are overconfident and place too much faith in their intuitions. He claims a lot of people find cognitive effort at least ‘mildly unpleasant’ and avoid it as much as possible.
So if you landed on 5p, well done – you obviously enjoy thinking.