IQ test: the hardest quiz 80% of people fail

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The world’s shortest IQ test has just three questions, but less than one in five people can answer all three correctly.

The world’s shortest IQ test has just three questions, but less than one in five people can answer all three correctly.

Dubbed the Cognitive Thinking Test, it comes from an article from 2005 by MIT Professor Shane Frederick, who sought to demonstrate the difference between rapid thought processes that occur with little conscious deliberation, and those that are slower and more reflective.

The test consists of three puzzle-type questions that are more difficult than it first appears, where the immediately obvious “right” answer is actually incorrect – if you stop and think.

“The three items on CRT are ‘easy’ in the sense that their solution is easily understood when explained, but achieving the correct answer often requires removing a wrong answer that comes ‘impulsively’ to mind.” , wrote Professor Frederick.

Of 3,428 people who took the test, only 17% answered all three questions correctly, more than half were wrong at least once, and a third got zero out of three. Even among students at MIT, the top performing group, less than half achieved all three good results.

Here are the 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 five machines five minutes to create five widgets, how long would it take 100 machines to create 100 widgets?

3. In a lake, there is a square of water lilies. 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?

Below are the answers most people guess, then the correct answers.

What most people guess:

1. 10 cents

2. 100 minutes

3. 24 days

As Professor Frederick noted, the intuitive answer to the first question is 10 cents, but this “impulsive” answer is wrong.

“Anyone who thinks about it even for a moment would agree that the difference between $ 1 and 10 cents is only 90 cents, not $ 1 as the problem says,” he wrote.

“In that case, detecting this error is tantamount to fixing the problem, because almost anyone who does not answer ‘ten cents’ gives, in fact, the correct answer. “

Here are the correct answers:

1. 5 cents

2. 5 minutes

3. 47 days

Presh Talwalkar, author of The Joy of Game Theory: An Introduction to Strategic Thinking and an expert in mathematical puzzles, explains further his blog, Mind Your Decisions.

1. “Let’s say the ball costs X. Then the bat costs $ 1 more, so it’s X + 1. So we have bat + ball = X + (X + 1) = 1.1 because together they cost $ 1.10. This means 2X + 1 = 1.1, then 2X = 0.1, so X = 0.05. This means the ball costs five cents and the bat costs $ 1.05. “

2. “If it takes five machines five minutes to create five widgets, then it takes a machine five minutes to create a widget (each machine makes a widget in five minutes). If we have 100 machines working together, each one can create a widget in five minutes. So there will be 100 widgets in five minutes.

3. “Every FORWARD day the patch doubles in size. So every BACKWARDS day means the patch size is reduced by half. So by day 47 the lake is half full.

Interestingly, men scored “significantly higher” than women on the CRT, although there was “no significant difference between the sexes” on other measures, including the automated cognitive test ( ACT), the Wonderlic Personnel Test (WPT), the Need for Cognition (NFC) scale, and the SAT College Entrance Test.

“Even if we focus only on respondents who gave the wrong answers, men and women differ. Women’s mistakes tend to be intuitive, while men make a wider variety of mistakes, ”Professor Frederick wrote.

“For example, women who miss the ‘widgets’ problem almost always give the wrong intuitive answer’ 100 ‘, while a small fraction of men give unexpected wrong answers, such as’ 20′ or ‘500’ or ‘ 1 ”. “

He added: “For each CRT item, the ratio of ‘intuitive’ errors to ‘other’ errors is higher for women than for men. Thus, the data suggests that men are more likely to reflect on their responses and less inclined to follow their intuitive responses.

He also noted an unusual finding: CRT scores were more closely correlated with “time preferences” for women than for men, but more closely related to “risk preferences” for men than for women.

“This result was not expected and does not suggest any obvious explanation,” he wrote, noting that “the only related finding I am aware of” was a 1990 study which found that “girls’ patience preschool age was strongly linked to their later SAT scores, but the preschool boys ‘patience was not’.

“Expressed freely, being intelligent makes women patient and men take more risks,” Professor Frederick wrote.

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