Let’s play a little game. Let’s see if you can outsmart some of the students at the country’s most prestigious institutions. Read the following question and see if you can get the correct answer:

A bat and ball cost $1.10.

The bat costs one dollar more than the ball.

How much does the ball cost?

Got it? 10 cents, right? Wrong. The correct answer is actually five cents.

“Huh?” you may be wondering. Here’s the explanation from Behavioral economist Daniel Kahneman and the book, “Thinking, Fast And Slow“:

A number came to your mind. The number, of course, is 10: 10¢. 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 10 ¢, then the total cost will be $1.20 (10¢ for the ball and $1.10 for the bat), not $1.10. The correct answer is 5¢. 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.

Many thousands of university students have answered the bat-and-ball puzzle, and the results are shocking. More than 50% of students at Harvard, MIT, and Princeton gave the intuitive—incorrect—answer. At less selective universities, the rate of demonstrable failure to check was in excess of 80%. The bat-and-ball problem is our first encounter with an observation that will be a recurrent theme of this book: many people are overconfident, prone to place too much faith in their intuitions. They apparently find cognitive effort at least mildly unpleasant and avoid it as much as possible.

Still confused? Don’t worry, it took this author about 10 minutes of thinking through it to figure it out. Think about it this way: the problem doesn’t say that the bat costs *exactly* $1…just that it costs an *additional *$1. So if the ball costs 10 cents, you’d be paying $1.10 for the bat alone. Instead, the ball has to cost five cents so that you’re only paying $1.05 for the bat.

The question isn’t anything new. In fact, it gained traction in December 2012 on sites like Business Insider. But it has recently started popping up again.

Pass it on and see if you can stump your friends.

Now take our poll and tell us how you did (be honest):