Here's The World's Shortest IQ Test And Only 17% Of People Can Pass It

By Dave Basner

May 15, 2020

Do you think you're pretty smart? Well here's an IQ test to find out if you really are. It's called the Cognitive Reflection Test and the three-question long quiz is part of a research paper by MIT professor Shane Frederick. Frederick gave his test to 3,000 people from all different types of educational backgrounds and only 17 percent were able to correctly answer all three questions. The questions seem simple, yet they require more thought than expected. Frederick explained in more academic terms, "The three items on the CRT are 'easy' in the sense that their solution is easily understood when explained, yet reaching the correct answer often requires the suppression of an erroneous answer that springs 'impulsively' to mind."

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 make five 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?

Were these your answers?

1. 10 cents

2. 100 minutes

3. 24 days

If so, congrats! You went three for three... in being wrong. Those are actually the most common answers that were guessed, but none of them are right.

The actual answers are:

1. 5 cents

2. 5 minutes

3. 47 days

Here's why:

Professor Frederick wrote about the first question saying, "Anyone who reflects upon it for even a moment would recognize that the difference between $1 and 10 cents is only 90 cents, not $1 as the problem stipulates. In this case, catching that error is tantamount to solving the problem, since nearly everyone who does not respond '10 cents' does, in fact give the correct response." You could also do some simple algebra to answer it. The ball costs X amount and the bat is $1 more, or 1 + X. In an equation, that would be written X + X + 1 = 1.1. That can also be shown as 2X + 1 = 1.1. Subtract 1 from both sides and 2X = 0.1. Divide by 2 and that gives you X = 0.05 so the ball is worth a nickel and the bat is $1.05.

In the second question, since five machines take five minutes to make five widgets, it means one machine can make one widget in five minutes. Just apply that to 100 machines with the same logic and that means they can make 100 widgets also in five minutes.

And for that final question, if every day the patch doubles, then the day before it covered the whole lake, it covered half the lake. That's why it is day 47.

Do you feel smart?

Photo: Getty Images

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