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Only 17% of people can pass this 3-question IQ test on the first try. Can you?

Developed by a Yale professor, this simple test reveals a lot about how you think—and only 17% of people get it right.

IQ test, cognitive reflection test, critical thinking, brain teasers, logic puzzles, psychology, System 1 thinking, problem solving

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By Adam Albright Hanna,
Adam Albright Hanna
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GOOD Staff
GOOD Staff
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Sep 18, 2025

It’s been called the world’s shortest IQ test, and despite its apparent simplicity, only about 17% of people answer all three questions correctly on their first try. The Cognitive Reflection Test (CRT) isn’t about measuring knowledge; it’s about measuring how you think.

The test was introduced in a 2005 paper in the Journal of Economic Perspectives by Yale professor Shane Frederick. It's designed to test your ability to override a quick, intuitive gut reaction and engage in deeper, more analytical thought.

Want to try it yourself?

IQ test, cognitive reflection test, critical thinking, brain teasers, logic puzzles, psychology, System 1 thinking, problem solving Woman sits in front of her computer thinkingCanva

Here are the three questions:

  1. A bat and a ball together cost $1.10. The bat costs $1.00 more than the ball. How much does the ball cost?
  2. If it takes five machines five minutes to make five widgets, how long would it take 100 machines to make 100 widgets?
  3. In a lake, there is a patch of lily pads. Every day, the patch doubles in size. If it takes 48 days for the patch to cover the entire lake, how long would it take for the patch to cover half of the lake?

The Answers and Why They're So Tricky

If you answered 10 cents, 100 minutes, and 24 days, you’re in the majority—and you’ve fallen for the trap. Those are the common intuitive answers. The correct answers are 5 cents, 5 minutes, and 47 days.

IQ test, cognitive reflection test, critical thinking, brain teasers, logic puzzles, psychology, System 1 thinking, problem solving Woman proudly shows testy resultsCanva

Here's the breakdown:

  • The Bat and Ball: If the ball cost 10 cents, the bat (at $1.00 more) would cost $1.10, for a total of $1.20. The correct math shows the ball is 5 cents and the bat is $1.05.
  • The Widgets: The rate of production is one widget per machine every five minutes. Therefore, 100 machines can produce 100 widgets in the same five-minute timeframe.
  • The Lily Pads: Since the patch doubles in size every day, it must have been half its final size just one day before it covered the whole lake—on day 47.

The Science of Your Brain

IQ test, cognitive reflection test, critical thinking, brain teasers, logic puzzles, psychology, System 1 thinking, problem solving An artistic representation of the brainCanva

This test brilliantly illustrates the two modes of thinking identified by Nobel Prize-winning psychologist Daniel Kahneman. System 1 is our fast, automatic, intuitive thinking, which gives us the quick (but wrong) answers. System 2 is our slower, more deliberate, and analytical thinking, which is required to solve the puzzles correctly.

As Frederick explains, the test measures how we make decisions based on instinct versus analysis. “System 1 thinkers respond spontaneously, often making mistakes, while System 2 thinkers engage in effortful thought processes,” he wrote.

@veritasium

The science of thinking #psychology

Frederick's research found that those with stronger cognitive reflection skills (System 2 thinkers) tend to be more patient and willing to take calculated risks. His work aims to understand the real-world impact of our cognitive styles, noting, “Despite the diversity of phenomena related to IQ, few have attempted to understand—or even describe—its influences on judgment and decision making.”

So, whether you passed the test or not, it offers a fascinating glimpse into the constant tug-of-war between gut reaction and careful thought that happens inside our brains every day.

This article originally appeared earlier this year.

brain teaserscognitive reflection testcritical thinkingiq testlogic puzzlesproblem solvingpsychologysystem 1 thinkingpast events

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