3-Question IQ Test

The viral “3 Question IQ Test” is everywhere – shared as the world’s shortest IQ test that separates “geniuses” from everyone else in under a minute. Fun? Absolutely. But this quiz is not a clinical IQ test. It’s the Cognitive Reflection Test (CRT), created by psychologist Shane Frederick at Princeton (2005) to measure how well you can override your first, intuitive answer and switch into slower, more reflective reasoning what popular psychology calls System 2 thinking (Frederick, 2005; Kahneman, 2011).

Below you can try the three items, see the explanations, and learn how the CRT differs from a real IQ test.

Take the 3-Question Test

These aren’t trick questions, but they’re designed to tempt you into a quick, wrong response. Take a breath and think it through.

Question 1: Bat & Ball

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?

Question 2: Machines & Widgets

If 5 machines take 5 minutes to make 5 widgets, how long would 100 machines take to make 100 widgets?

Question 3: Lily Pads

In a lake, a patch of lily pads doubles in size every day. If it takes 48 days to cover the whole lake, how long to cover half the lake?

Answers (with step-by-step reasoning)

Q1: Five cents.

The common gut answer is 10¢—but that would total $1.20 ($1.10 bat + $0.10 ball).

Let the ball be x; then the bat is x + $1.00.

Total: x + (x + 1.00) = 1.10 → 2x = 0.10 → x = 0.05.

So the ball = $0.05 and the bat = $1.05 → together $1.10.

Q2: Five minutes.

5 machines → 5 widgets in 5 minutes means each machine produces 1 widget in 5 minutes.

With 100 machines running in parallel, you still need 5 minutes to make 100 widgets.

Q3: Forty-seven days.

Because the patch doubles every day, the lake is half covered the day before it’s fully covered.

So if the lake is full on day 48, it’s half full on day 47.

Scoring: 0–3 correct. In Frederick’s original study, even students at elite universities performed imperfectly; only about 17% answered all three correctly (Frederick, 2005). That’s the design: each item elicits an appealing, intuitive wrong answer (10¢, 100 minutes, 24 days) that must be overridden by reflection.

What the CRT Actually Measures

The CRT is a thinking-style check, not a comprehensive ability test. It taps your tendency to:

• Notice a tempting answer that “feels right”…then question it, slow down, and engage analytic reasoning to verify.
• In the dual-process framework popularized by Kahneman, the CRT pits System 1 (fast, automatic, intuitive) against System 2 (slow, deliberate, rule-based) (Kahneman, 2011). People who score higher on the CRT, on average, show more reflection and fewer common reasoning errors in experimental tasks (Frederick, 2005).

Is It an IQ test?

No. A real IQ assessment samples multiple domains: verbal comprehension, visual-spatial reasoning, working memory, and processing speed via many subtests and standardized administration. It’s normed by age and interpreted by trained professionals under testing standards. The CRT has three items, large practice effects, and no age norms. It correlates modestly with some ability measures, but it is not a substitute for the WAIS, WISC, or Stanford-Binet.

Why So Many People Miss These Questions

The CRT items are classic cognitive illusions. Like visual illusions, they exploit shortcuts our brains use to save effort:

• Attribute substitution: we unconsciously swap a hard question for an easier one (e.g., “How can $1.10 split into ‘$1 more’?” → “10¢ and $1.00”).
• Fluency bias: numbers like “100” invite linear thinking (“100 machines → 100 minutes”).
• Exponential blind spot: we’re poor at doubling growth, so we split the days in half instead of subtracting one.
• The cure is simple but not always easy: pause, translate the words into structure (an equation, a rate, a doubling timeline), and check whether your answer satisfies all the conditions.

What a Real IQ Test Looks Like (Quick Compare)

How to Use the CRT

Enjoy it as a brainteaser. It’s great for classrooms, training sessions, or a quick thinking warm-up.

Don’t diagnose yourself. It doesn’t measure creativity, EQ, personality, or your full cognitive ability.

Expect practice effects. Once you know the items, your score tells you you’ve seen the items.

Apply the habit. In real decisions, build the CRT mindset: slow down on “obvious” answers, check the math, and ask, “What assumption am I making?”

FAQs

Is the 3-Question IQ Test legit?

It’s legit as a research tool (the CRT) that measures cognitive reflection, not as a full IQ test (Frederick, 2005).

Who invented it?

Psychologist Shane Frederick at Princeton, published in the Journal of Economic Perspectives (2005).

What does a perfect score mean?

You correctly overrode three common intuitive traps today. It doesn’t diagnose “genius,” and performance can change with attention, practice, and context.

Does speed matter?

The CRT is untimed; response time isn’t part of the score. Many people need to slow down to answer correctly. That's the point.

How does it compare to the Mensa or WAIS tests?

Mensa admissions and clinical IQ testing rely on standardized, age-normed batteries administered by professionals; the CRT does not meet those standards.

Bottom Line

The 3-Question IQ Test is a clever, memorable snapshot of a thinking habit: can you resist the easy answer and work through the logic? Use it for fun and self-reflection. If you want a comprehensive view of your cognitive strengths, look at a standardized IQ assessment and remember that real-world success blends reflection with knowledge, motivation, and good judgment.

References

1. Frederick, S. (2005). Cognitive reflection and decision making. Journal of Economic Perspectives, 19(4), 25–42.
2. Kahneman, D. (2011). Thinking, fast and slow. Farrar, Straus and Giroux.