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World's Shortest IQ Test

Updated: Dec 2, 2023

It will reveal how average your intelligence is in just 3 questions. Why not give it a go?

Neon sign depicting a question mark

The Cognitive Reflection Test is dubbed the world’s shortest IQ test because it consists of just three questions. It assesses your ability to identify that a simple problem (bear that in mind!) can actually be harder than it first appears.

Here are the three questions:

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 is what a lot of people guess:

1. 10 pence

2. 100 minutes

3. 24 days

These answers are all wrong. Want another go?

When you're ready, scroll down for the correct answers, and how you get to them:

1. The ball would actually cost 5 pence or 0.05 pounds.

If the ball costs X, and the bat costs £1 more, then it will be: X + £1

Therefore: Bat+ball = X + (X+1) = 1.1

Thus: 2X + 1 = 1.1, and 2X = 0.1

X = 0.05

2. It would take 5 minutes to make 100 widgets.

Five machines can make five widgets in five minutes; therefore one machine will make one widget in five minutes too. Therefore if we have 100 machines all making widgets, they can make 100 widgets in five minutes.

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

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

In a survey of almost 3,500 people, 33 percent got all three wrong, and 83 percent missed at least one. While this IQ test has its shortcomings – its brevity, and lack of variation in verbal and non-verbal reasoning - only 48 percent of MIT students sampled were able to answer all three correctly.

How did you get on? And why not test your friends and family by forwarding this page to them...?


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