Puzzles
A bat and ball cost $1.10 together. The bat costs a dollar more. What's the ball?
Almost everyone's first answer is 10 cents. It feels obviously right, arrives instantly, and is wrong. Can you find the actual price of the ball, and see why your gut answer fails the problem's own condition?
Reveal the answer
The ball costs 5 cents (and the bat $1.05 — exactly one dollar more, for a total of $1.10). Ten cents fails because it would make the bat only 90 cents more, not a full dollar. Psychologist Shane Frederick published this as the flagship item of his three-question Cognitive Reflection Test in 2005: a measure not of intelligence but of whether people pause to check a confident, fast, wrong intuition before answering.
— Shane Frederick, Cognitive Reflection and Decision Making — Journal of Economic Perspectives, 2005