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World's shortest IQ test reveals how intelligent you are in just 3 questions

True intelligence is often more about perspective, observation, and intuition than classroom test scores. Over the past century, researchers have explored unconventional ways to measure intelligence. IQ tests, for example, are now common tools for recruiting top candidates in prestigious institutions. One test gaining widespread attention is the "world’s shortest IQ test," known as the Cognitive Reflection Test (CRT), which consists of just three questions.

CRT was originated by Yale University Professor Shane Frederick who published a report about it in the Journal of Economic Perspectives in 2005. The three-item cognitive test was designed to measure a person’s cognitive ability through their psychometric scores. These were the three mind-boggling questions of the test:

1.    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?

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?

The correct answers for the questions, according to the paper, were “5 cents,” “five minutes,” and “47 days” respectively. The explanations for these answers are stunningly quite simple, as Dr. Lyndon Walker, a former statistics and finance lecturer, tells in a YouTube video. For the first question, an impulsive response might be “10 cents” as the quiz-taker might simply subtract 10 cents from \$1.10 to obtain \$1.00. But this is not the correct way as the number 10 refers to cents while the number 1.10 refers to dollars. So, if one assumes the ball’s cost to be x dollars, the bat’s cost would be (x+1) dollars, hence the equation: x + (x + 1) = 1.10, which answers \$0.05, meaning 5 cents.

The second question is a bit trickier. Since 5 machines take 5 minutes to build 5 widgets, the quizzer might react to the question saying the time taken for 100 machines to build 100 widgets would be 100 minutes. That’d be incorrect. In actuality, if 5 machines take 5 minutes to build 5 widgets, it means that if there are 100 machines, then in every 5 minutes, each set of 5 machines will make 5 widgets, hence, totaling 100 widgets. Therefore, the correct answer is 5 minutes.

The third question is the most complex of all. If the patch doubles in size every day, and if it takes 48 days to cover the entire lake, then let’s assume the lake’s size is 2x. Since the size on the last day was double the size of the previous day, the previous day’s patch size was x. So, it took 48 minus one, that is 47 days to cover x, that is half the lake.

Researchers who first conducted this test mainly evaluated participants’ performance based on two factors: Time preference and risk preference, as per the paper. The CRT was carried out on 3,428 respondents in 35 separate studies over 26 months beginning in January 2003. Most respondents were undergraduates at various universities in the Midwest and Northeast who were paid \$8 to complete a 45-minute questionnaire.

Frederick mentioned in the report that another researcher Kahneman classified the psychology behind people’s responses into two categories: “System 1” and “System 2.” In the System 1 process, the individual answered spontaneously, without paying much attention. Whereas, in the System 2 process, people utilized their mental operations requiring effort, motivation, concentration, and the execution of learned roles. In most of these questions, the impulsive, that is, System 1 answers proved to be incorrect. For instance, the candidates who answered 10 cents for the first question, 100 minutes for the second question, or 24 days for the third question.

Adding to the explanation behind people’s responses to the three-item CRT, Frederick noted in the paper that people with high cognitive abilities usually live longer, earn more, have larger working memories, have faster reaction times, and are more susceptible to visual illusions. But till now, not many attempts have been made to determine this ability in people, except for CRT. “Despite the diversity of phenomena related to IQ, few have attempted to understand—or even describe—its influences on judgment and decision making,” wrote Frederick.

Editor's note: This article was originally published on July 27, 2024. It has since been updated.

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