Science & Tech

Greg Evans

Jul 24, 2024

IQ tests offer a formula that allows you to compare yourself to other people and see how average (or above average) your intelligence is.

The Cognitive Reflection Test (CRT) 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 can actually be harder than it first appears. The quicker you do this, the more intelligent you appear to be.

**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?

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**Here is what a lot of people guess:**

1. 10 pence

2. 100 minutes

3. 24 days

These answers would be **wrong**.

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 per cent got all three wrong, and 83 per cent 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 per cent of MIT students sampled were able to answer all three correctly.

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