Questions from the world’s shortest IQ test even stumped students at Yale and Harvard!
Maybe you have a dark sense of humor, or perhaps you failed your driver’s test—both are signs of intelligence, according to science. But how smart are you, really? The Cognitive Reflection Test (CRT), also known as the world’s shortest IQ test, claims it takes only three questions to tell if you’re a genius.
Developed in 2005 by Princeton psychologist Shane Frederick, this fast IQ quiz assesses your ability to process information slowly and rationally, rather than jumping to quick conclusions. In a 2024 paper published in the scientific journal PNAS, researchers wrote of the test, “Its items were intended to evoke erroneous intuitions that most would succumb to but which could be corrected by those who bothered to reflect upon or scrutinize them.”
Before you get started with this quick IQ test, we’ll give you a hint: Like the Mensa IQ test, the CRT includes questions that might not be as easy as they first seem. A 2005 study found that students attending some of the nation’s most prestigious universities (including Harvard and Yale) failed to get all three of these questions correct; only 17% received a perfect score.
Will you rank among the nation’s brightest? Read on for the world’s shortest IQ test and see if you’re able to crack it.
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Can you ace the world’s shortest IQ test?
Although it’s tempting to think that the shortest IQ test in the world is a definitive indicator of intelligence, that’s not the case. The CRT isn’t a clinical IQ test; it’s more of a brainteaser or a quiz that you can try your hand at.
Think you have what it takes? Give these three questions a shot and see how well you score. Best of luck!
Questions
These aren’t trick questions, but they aren’t exactly what they seem. So take your time!
1. The bat-and-ball problem
A bat and a ball cost $1.10 in total. The bat costs $1 more than the ball. How much does the ball cost?
2. The 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 water lily pad problem
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?
Once you think you have the solutions to these tough questions, check out the answers below to see how well you fared.
Answers
You’ve done the tricky math and have three numbers in mind. Let’s see how you did.
1. Five cents
A common guess—and most people’s very first response—is 10 cents. But take a second look, and you’ll realize that if that were the case, the total cost of the bat and ball would be $1.20, not $1.10. Remember, the bat costs $1 more than the ball, so if the ball were 10 cents, the bat would be $1.10, for a total of $1.20.
A 5-cent ball and a bat priced at $1.05 (which is $1 more than 5 cents) would total $1.10.
2. Five minutes
Although you might have answered 100 minutes, the actual time is less than that. Let’s look at the question again: The output of five machines is five widgets in five minutes. That means it would take five minutes for one widget machine to make one widget.
If you had 100 machines, they’d each make one widget in five minutes—for a total of 100 widgets.
3. Forty-seven days
At first, your gut might tell you to divide 48 days in half, leading to believe it’d take 24 days. But remember, the area of the lake covered in lily pads doubles every day. So a patch that covers half the lake would fully cover it in just one additional day. Subtract one day from 48 days, and what do you get? 47 days.
FAQs
What is the world’s shortest IQ test?
The world’s shortest IQ test, the Cognitive Reflection Test (CRT), uses three questions to tell if you’re smart enough to go toe-to-toe with bona fide geniuses. It seems easy at first, but it requires a closer look at the questions’ wording and demands careful reflection.
It’s not a clinical IQ test, mind you, but simply an interesting case study in how people tend to think.
How does the world’s shortest IQ test compare with traditional IQ tests?
Although it’s called the world’s shortest IQ test, CRT is more of a test of cognitive reflection. This means that the test evaluates the disposition of thinking rather than intelligence itself.
Meanwhile, traditional IQ tests are focused on mapping cognitive intelligence. “The CRT could be considered as an actual measure of rational thought, rather than as cognitive intelligence,” researchers from the University of Santiago de Compostela wrote in a study published in 2022 in Intelligence.
What are common mistakes people make when taking the world’s shortest IQ test?
One of the biggest mistakes is jumping to the obvious answer when a careful reflection reveals a different choice. Another mistake is not paying attention to the wording of the question, which has a different interpretation when you read it the second time.
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Sources:
- PNAS: “Cognitive reflection is a distinct and measurable trait”
- American Economic Association: “Cognitive Reflection and Decision Making”
- Intelligence: “Cognitive reflection, cognitive intelligence, and cognitive abilities: A meta-analysis”
