A bat and a ball cost 1.10 dollars together. The bat costs 1.00 dollar more than the ball. How much does the ball cost?
You have probably met this one before. Even people who have seen it still feel the wrong answer arrive first, which is precisely why it became famous.
Why almost everyone says ten cents
The ball costs 5 cents. If the ball were 10 cents, the bat would be 1.10 dollars and the total would be 1.20 dollars. At 5 cents for the ball, the bat is 1.05 dollars and the two add up to 1.10 dollars exactly.
This is the most studied trick question in psychology, and it belongs to a small set of items known as the cognitive reflection test. The interesting part is not that people get it wrong. It is that an answer arrives instantly, feels obviously right, and is not checked.
Getting this one right has less to do with arithmetic than with a habit. The people who answer correctly are usually not faster at the maths, they are the ones who paused and tested the number that showed up.
How to catch your own thinking errors
You cannot check every thought you have, and trying would be exhausting and useless. The skill is knowing which thoughts are worth a second look.
The fast answer is not the enemy. It is right most of the time, which is exactly why it goes unchecked in the cases where it is wrong. What you want is a cheap trigger that tells you when to slow down.
The most reliable trigger is the feeling of certainty arriving too quickly on a question that involves numbers, comparisons or anything phrased as more than. That combination is where intuition fails most often, and noticing it takes two seconds.
- Substitute your answer back into the original wording and check it holds
- Treat instant certainty on a numerical question as a warning sign
- Watch for the phrase more than, which is where the trap usually sits
- When a decision matters, write the check down rather than doing it mentally
These checks need a couple of uninterrupted seconds, which is precisely what a distracted environment removes. Our guide on how to improve focus and concentration covers how to get those seconds back. It opens in a new tab.
One question left, and it is a reading trap rather than a maths one.