How do you measure intelligence? How many GCSEs people have got? How far they took their education? Whether they can solve a Rubik's Cube? Or their ability to hold their own in a four-way conversation down the pub?

There is, of course, the standard IQ test, either professional or DIY, and this is a popular way to judge a person's intelligence.

But these tests are not quick - otherwise we'd get them inside Christmas crackers and use them to break the ice at parties.

This is why one particular intelligence test is gaining popularity. The Cognitive Reflection Test, known as "the world's shortest IQ test", was originally described by a psychologist in 2005 and has been a fascination of the media this week, particularly in America.

According to our colleagues at Mirror Online, it consists of just three questions. Before we tell you more about it, you can give it a go, below:

Question 1


The options are: 15p, 10p and 5p.

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How much does the ball cost?


Question 2


The options are: 100 minutes, 50 minutes and five minutes.

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How long would it take the machines to make 100 widgets?


Question 3



The options are: 24 days, 47 days and 36 days.

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How long does it take for the patch to cover half of the lake?


So, how confident are you?

Before we get to the answers, we'd like to point out that the aim of the test is to assesses individuals' ability to suppress an intuitive and spontaneous wrong answer in favour of a reflective and deliberative right answer.

So, in theory, if you have got anything wrong, it may only be because you were trying to answer a bit too quickly and, with a bit more time, you may well have figured it out.

Here are the answers.

Question 1

The odds are your first answer to this was 10p. This, however, is the wrong answer. If the ball is 10p and the bat is £1 more then the bat costs £1.10 - but that comes to a total of £1.20, not £1.10.

Don't rush. Take a breath, step back and give your brain a moment.

You realise that the £1.20 total is too high so allow your brain to go to the next lowest, 5p, and realise that if the ball cost 5p and the bat costs £1 more at £1.05 then the total is £1.10 and so that is the right answer.

You can also work this out using basic algebra (though this takes a bit longer).

But here's the algebra anyway. And we'll go through it step by step.

Let's say the ball costs X and the bat costs £1 more - so that's £1 + X for the bat.

Total cost = £1.10 = bat + ball = (£1 + X) + X

You can also write that as £1 + X + X or £1 + 2X

So you've got this equation:

£1 + 2X = £1.10

If you take £1 away from each side, you get this:

2X = £0.10 or 2X = 10p

So two balls cost 10p and therefore one ball costs 5p.

Question 2

It's tempting, if answering these quickly, to guess 100 minutes but, again, this is wrong.

So, as before, don't rush, trust your brain.

Five machines make five widgets in five minutes.

The machines are working at the same time, so each of them takes five minutes to make a widget.

And if one machine takes five minutes to make a widget then 100 machines working at the same time will each take five minutes to make a widget.

So 100 machines make 100 widgets in five minutes. Bingo!

Question 3

If your first thought is 24 days, take another breath and read the question again.

If the patch doubles in size each day going forward, it would halve in size going backwards a day. So, on day 47, the lake is half full.

So, how did you do?

If you got all three right, then well done you! But please don't worry if you got any wrong, or indeed all of them.

No homework for tonight. Class dismissed.