Can You Pass the World’s Shortest IQ Test?

Updated: Mar. 13, 2024

These questions even stumped students at Yale and Harvard

So, you might have a dark sense of humor or failed your driver’s test—all 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 only takes three questions to tell if you’re a genius. Talk about a quick IQ test!

Developed in 2005 by Princeton psychologist Shane Frederick, the quiz assesses your ability to process information slowly and rationally, rather than jumping to quick conclusions. “In order to succeed in the CRT, you must spend time reflecting on your answer and question your intuitive response,” IFL Science explains.

Before you get started with this brain game–like test, we’ll give you a quick hint: The questions might not be as easy as they first seem (similar to these Mensa IQ test questions). 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.

Can you ace this quick IQ test?

Think you have what it takes? Give it a shot! Here are the three questions:

1. 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. If it takes 5 machines 5 minutes to make 5 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?

Check out the answers below, and best of luck! By the way, see if you can solve these challenging riddles after you get the answers.


1. Five cents. If you guessed 10 cents, you’re not alone. However, if that were the case, the bat and ball would cost $1.20—not $1.10. On the other hand, 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. Since the question reveals that it would take 5 minutes for 1 widget machine to make 1 widget, you can determine that it would also take 5 minutes for 100 widget machines to make 100 widgets.

3. Forty-seven days. At first, your gut might tell you it would take 24 days. But remember: Since the area of the lake covered in lily pads doubles every day, 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. Now that’s a tricky math puzzle.

Next, see if you can wrap your mind around these challenging brain teasers.


  • IFL Science: “The World’s Shortest IQ Test Is Just Three Questions Long, But Almost No One Can Get Them All Right”