Only smartest people can pass brutal three-question IQ test

More than 80 percent of people fail this near-impossible IQ test, thought to be the shortest in the world, with just three questions. The brutal Cognitive Reflection Test had a pass rate of just 17 % when it was launched as part of a research paper in 2005 by MIT Professor Shane Frederick.

Out of a test group of 3,000 people from various educational backgrounds, even those from top Universities like Harvard and Yale struggled, CheshireLive reports. However, Professor Frederick explained: “The three items on the CRT are ‘easy’ in the sense that their solution is easily understood when explained, yet reaching the correct answer often requires the suppression of an erroneous answer that springs ‘impulsively’ to mind.” Having recently resurfaced online, people are once again attempting it to see how they fare. 

The questions 

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?
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?

These are the three most common answers, which are actually incorrect:

1. 10 cents
2. 100 minutes
3. 24 days

Professor Frederick pointed out: “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.”

The correct answers:

1. Five cents

2. Five minutes

3. 47 days

Explanations of the answers

Presh Talwalkar, the author of The Hoy of Game Theory: An Introduction to Strategic Thinking, explained the answers on his blog, Mind Your Decisions.

1. 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 five cents and the bat costs $1.05
2. If it takes five machines five minutes to make five widgets, then it takes one machine five minutes to make one widget (each machine is making a widget in five minutes). If we have 100 machines working together, then each can make a widget in five minutes. So there will be 100 widgets in five minutes.
3. 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.