[stephenkhoo]

Consider, for example, the following puzzle. 1. A bat and a ball cost $1.10 in total. The bat costs $1.00 more than the ball. How much does the ball cost? What’s your instinctive response? I’m guessing that it is that the ball must cost 10 cents. That can’t be right, though, can it? The bat is supposed to cost $1.00 more than the ball. So if the ball costs 10 cents, the bat must cost $1.10, and we’ve exceeded our total. The right answer must be that the ball costs 5 cents. Here’s another question: 2. If it takes 5 machines 5 minutes to make 5 widgets, how long would it take 100 machines to make 100 widgets? The setup of the question tempts you to answer 100. But it’s a trick. One hundred machines take exactly the same amount of time to make 100 widgets as 5 machines take to make 5 widgets. The right answer is 5 minutes. These puzzles are two of the three questions that make up the world’s shortest intelligence test.1 It’s called the Cognitive Reflection Test (CRT). It was invented by the Yale professor Shane Frederick, and it measures your ability to understand when something is more complex than it appears—to move past impulsive answers to deeper, analytic judgment