# World's shortest IQ test only has three questions - but 80 percent fail it

If you've ever wanted to test your intelligence, but can't be bothered to sit through a lengthy IQ test, we may have the perfect solution for you.

The world's shortest IQ test is made up of just three maths questions and shouldn't take too long to complete.

But be warned - it's pretty tough!

Called the Cognitive Reflection Test, the quiz isn't new, but was originally part of a research paper published in 2005 by MIT professor Shane Frederick. This paper has recently resurfaced online, leaving many keen to give it a go.

As part of his research, Professor Frederick had more than 3,000 participants from a range of educational backgrounds complete the test - and even those attending top American universities such as Yale and Harvard struggled to work out all the answers.

Of all those who took part only 17 percent managed to score three out of three on the test, meaning 83 percent of people failed - how will you fare?

Speaking about the test, Professor Frederick, said: "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."

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Here's a look at 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?

These are the three most common answers that people guess - but they are actually incorrect.

1. 10 cents

2. 100 minutes

3. 24 days

Professor Frederick adds: "Anyone who reflects upon it for even a moment would recognise 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."

1. 5 cents

2. 5 minutes

3. 47 days

Still puzzled by all of this? Thankfully, Presh Talwalkar, the author of The Hoy of Game Theory: An Introduction to Strategic Thinking explained how to work out the correct answers on his blog, Mind Your Decisions.

1. Say the ball costs X. Then the bat costs \$1 more, so it is 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 5 cents and the bat costs \$1.05

2. If it takes 5 machines 5 minutes to make 5 widgets, then it takes 1 machine 5 minutes to make 1 widget (each machine is making a widget in 5 minutes). If we have 100 machines working together, then each can make a widget in 5 minutes. So there will be 100 widgets in 5 minutes.

3. Every day FORWARD the patch doubles in size. So every day BACKWARDS means the patch halves in size. So on day 47 the lake is half full.

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