Take the world’s shortest IQ test!

The Cognitive Reflection Test (CRT), developed in 2005 by psychologist and Yale School of Management professor Shane Frederick, is the world’s shortest IQ test, comprised of only three questions.

In a paper published in The Journal of Economic Perspectives, Frederick explains that he picked the three questions because they were all “found to yield impulsive erroneous responses” — the questions make it easy for people to quickly jump to conclusions. In other words, the CRT was designed to test your ability to ignore your intuitive gut response and think more rationally.

After you’ve taken the test, scroll down for the answers.

No cheating!!!

Here Are the Questions

1. The Bat and Ball Problem

A bat and a ball together cost $1.10. The bat costs $1 more than the ball. How much does the ball cost?

2. The Widget-Making Machine Problem

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

3. The Size-Double Lily Pad Patch Problem

There is a patch of lily pads in a lake. 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 the lake?

Scroll down for the answers to the questions.

Here Are the Answers

1. The ball costs 5 cents.

You probably guessed 10 cents, didn’t you? A ball that costs 5 cents plus a bat that costs $1.05 will set you back $1.10. And $1.05 is exactly $1 more expensive than 5 cents. A Princeton study found that people who answered 10 cents were significantly less patient than those who got it correct.

2. It would take 100 machines 5 minutes to make 100 widgets.

Your gut might tell you the answer is 100 minutes. From the question, we know that it takes 5 minutes for 1 machine to make 1 widget. Thus, it would take 5 minutes for 100 machines to make 100 widgets. (Check out a similar, if not more difficult problem, here.)

3. The lily pads would cover half the lake in 47 days.

You might have guessed 24 days. It seems intuitive to halve the number of days because you’re halving the size of the lilypad patch. But if the area of the lake covered in lilypads doubles every day, it would only take one day for it to go from being half covered to fully covered. Take one day away from 48 days and you’re left with 47. (We have a similar problem here, too.)

Before introducing the test to the world in 2005, Frederick tested the CRT on 3,428 respondents in 35 separate studies over a 26-month period beginning in January 2003. Only 17% of students from the top universities in the world (like Yale and Harvard) got a perfect score. People who score high are less vulnerable to biases in thinking.

So how did you do?

H/t FOTM‘s josephbc69

Here’s something depressing about America’s college graduates:

See also:


25 responses to “Take the world’s shortest IQ test!

  1. Clever. Now I have a question….. If a respondent answers all three questions correctly, what is his/her IQ?

    Liked by 1 person

  2. I know of a shorter IQ test.

    Did you vote for Hillary Clinton?

    Liked by 6 people

  3. A Facebook reader of FOTM wrote this comment: ” Still don’t understand the ball and bat one unless they’re throwing in $0.05 for tax”

    Here’s my answer:

    “The bat (X) costs $1 MORE THAN the ball (Y) means that the bat costs $1 + Y. Both bat and ball together would then cost $1 + Y + Y (where $1+Y = cost of bat). Since we are told the cost of both bat and ball is $1.10, that means the bat (X) costs $1.05 and the ball (Y) costs $0.05, making bat(X)+ball(Y) = $1.10.”

    Liked by 1 person

  4. To me the bat is Donald Trump, the ball is Killary Rotten Clinton, bases full, HOME RUN,!!

    Liked by 1 person

  5. Pretty fun. The widget question is ambiguous, as it does not clearly state that five machines make five widgets in five minutes. My immediate question was “do they mean five minutes per widget, or five widgets each?”

    Liked by 1 person

    • Since there is no “each” in the phrase “If it takes 5 machines 5 minutes to make 5 widgets”, I understood it to mean exactly that — 5 machines took a total of 5 minutes to make a total of 5 widgets — which, in turn, means that each machine took 5 minutes to make 1 widget. That, in turn, means that no matter how many machines, each machine still takes 5 minutes to make 1 widget. Conclusion: It takes 100 machines 5 minutes to make 100 widgets.

      The trap is the number “100” machines. It’s a distraction. Even if the question were “How long would it take 1 million machines to make 1 million widgets,” the answer would still be “5 minutes”.


      • That’s exactly right (the trap). You can just think logically about factories and industrialization for a common sense view: the whole idea about buying more machines or hiring more workers is to get more work done or product made in the same amount of time. Conversely, if you took the question to the absurd and asked “what about a million machines?”, it would be pretty clearly absurd to think it would then take a million minutes; why then would the owner buy a million machines? It’s always to reduce the time required and/or to increase production.

        That said, one can’t definitively say from the question that a single machine can produce a widget in 5 minutes unless we’re also told that all 5 machines were working simultaneously and started at the same time… which is the logical assumption. So you have to go to common sense and logic about what you know.

        BTW, my initial thought on the 1st question was $0.10 for the ball, but a quick calculation showed that to be illogical. So I did a quick re-calc of $0.05 and $1.05 (after dismissing the possibility of $0.01 and $1.01), which worked. If it hadn’t, I was ready to do a little algebra as you showed… ;~)

        The 3rd question was easy for me, as I do a lot of base-2 math for computer stuff. It’s also involved in a pet peeve of mine, saying things multiply by “folds” as in “4-fold increase”. Which does NOT mean 4x more. It means, technically, 2^4, or 16x more. Each time you raise the n value in 2^n by one, you double the result. Just as when you fold a sheet of paper once (in half) — you now have 2 folds. Do it again and you have four. A third time and you have eight, thus doubling each fold… It’s a bit like compounded interest, a favorite of mine. So in the question above, the day before the pond was covered, it was exactly half covered.

        Liked by 1 person

    • I confused that one also; I presumed that each machine was producing 5 in 5 minutes. The other did take careful thought for me.

      Liked by 1 person

    • This test has been, uh, tested on thousands of people before it made it onto FOTM. This issue is likely an implicit element of the test.


  6. I’m always a little bit afraid to take tests like this, in case I disappoint myself. This was a pretty good little test, however, and fun. I’m going to try to remember these for dinner parties.

    Liked by 2 people

  7. Don’t laugh.

    Questions two and three I got easily, but I have to admit I blew the first one.

    LOL – I guess that means I am dumb enough to get into Harvard. 😦

    Full disclosure: I have heard the third question before.

    Liked by 1 person

  8. Reblogged this on kommonsentsjane and commented:

    Reblogged on kommonsentsjane/blogkommonsents.

    For your information.


    Liked by 1 person

  9. i got the widget answer right but that’s about it lol

    Liked by 1 person

  10. Stephen T. McCarthy

    I got them all right, but ONLY because I knew ahead of time that whatever the correct answers were, they’d be different from what seemed “obvious”. Because I was forewarned that “the questions make it easy for people to quickly jump to conclusions”, I actually thought longer about each question than I normally would have. Had I answered quickly and impulsively, I’d have gotten all 3 of them wrong.

    Math was always my worst subject. Followed by English. Over the years, I became a voracious reader and got a whole lot better at English. But my math still stinks.

    ~ D-FensDogG
    STMcC Presents ‘Battle Of The Bands’

    Liked by 1 person

  11. One of three right. Im an idiot.

    Liked by 1 person

  12. 1 for 3. Duh.

    Here’s a fun one

    Liked by 1 person

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