Here’s a simple arithmetic question: “A bat and ball cost $1.10. The bat costs $1 more than the ball. How much does the ball cost?” The vast majority of people respond quickly and confidently, insisting the ball costs 10 cents. This answer is both incredibly obvious and utterly wrong. (The correct answer is five cents for the ball and $1.05 for the bat.) What’s most impressive is that education doesn’t really help; more than 50% of students at Harvard, Princeton and the Massachusetts Institute of Technology routinely give the incorrect answer.