The Cognitive Reflection Test: The world’s shortest IQ test, that most people fail

The world’s shortest IQ test — just three questions — has gone viral again and thousands are rushing to see if they are in the top 20 per cent.

The Cognitive Reflection Test, created in 2005 by MIT psychology professor Shane Frederick, has reappeared on TikTok, stumping many with its seemingly straightforward puzzles.

Frederick asked 3428 people the same three questions and found only 17 per cent of people got them all correct.

Another 33 per cent got them all wrong and the remainder could answer one or two correctly.

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TikTok user @chibimallo has previously posted about the test, attempting to explain how it works.

Take the world’s shortest IQ test

(Answers below.)

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 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?

Here’s what you probably answered

• 1. 10 cents

•2. 100 minutes

• 3. 24 days

What the real answers are

1. The ball would actually cost five cents.

With this equation, you need to think outside the box.

If the ball costs 10 cents, then the bat would cost $1.10 as it would be a dollar more.

To keep the total at $1.10 then the ball would have to cost 5 cents and the bat would cost $1.05.

2. It would take five minutes to make 100 widgets.

If it takes five machines five minutes to make five widgets, then it will take one machine five minutes to make one widget.

Therefore if 100 machines were all making widgets, it would take five minutes.

3. It would take 47 days for the patch to cover half of the lake.

The patch is doubling in size each day going forward, so it would make sense that it’s halving in size going backwards.

This means that on day 47, the day before it covered the entire lake, it would be halfway covered.

This article was first published by the NZ Herald and is republished here with permission.