World's shortest IQ test only has three questions but 83% of people fail it

Many of us enjoy watching quiz shows, confidently answering questions from the comfort of our living rooms and believing we could outshine the contestants.

However, true intelligence goes beyond quick reactions we might have developed from gaming, and a deceptively simple IQ test has been designed to challenge even the most confident minds.

Originally published in 2005 by professor Shane Frederick, the Cognitive Reflection and Decision Making test consists of just three questions.

A person taking a test (Pixabay)

Despite its brevity, it has proven remarkably difficult — when Frederick tested 3,000 participants, only 17 percent managed to answer all three correctly, meaning a staggering 83 percent failed.

With the published CRDM test still available to view online today, more have been trying it out for themselves. With both sets of questions and answers below, give them a try for yourself to see if you can join the ranks of Frederick's elite 17 percent. If you use AI for help, it doesn't count.

The three questions of the Cognitive Reflection and Decision Making test are as follows:

• Question 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?
• Question 2: If it takes five machines five minutes to make five widgets, how long would it take 100 machines to make 100 widgets?
• Question 3: In a lake, a patch of lily pads doubles in size every day. If it takes 48 days for the patch to cover the entire lake, how long would it take to cover half the lake?

Now, for the answers. Most people instinctively answer ten cents, 100 minutes, and 24 days.

However, the correct answers are five cents, five minutes, and 47 days.

Explaining the first question in his publication, Professor Frederick noted: "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."

Answering a test paper (Pixabay)

For those still unsure, Presh Talwalkar from Mind Your Decisions provides a more detailed breakdown.

Addressing question 1, he says: "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".

When solving question 2, he answered: "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."

Finally, to answer question 3, Talwalkar explained: "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."

This test highlights how our brains often default to intuitive but incorrect answers. If you answered all three correctly, you’re among the top 17 percent. If not, don’t worry — this simple yet effective test serves as a great reminder to slow down and think critically.