While you’re in the gym, there’s a lot of waiting: between sets or for equipment, for example. So why not use this time productively and take the world’s shortest IQ test, which has just three questions. Easy no?

The test, known as the cognitive thinking test, was originally part of a research paper published in 2005 by MIT Professor Shane Frederick. Although it only has three questions, don’t be fooled by its brevity. It still managed to baffle most of the people to whom Frederick initially gave it. Specifically, 83% of people who took the test Fredrick, which includes students from top US universities such as Yale and Harvard, struggled to find the answers.

â€œThe three items on CRT are ‘easy’ in the sense that their solution is easy to understand when explained, but achieving the correct answer often requires removing a wrong answer that comes ‘impulsively’ to mind. “said Frederick.

So, are you ready to take the test? Here are the three 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 create five widgets, how long would it take 100 machines to create 100 widgets?
3. In a lake, there is a square of water lilies. 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?

See, we told you it was easy. Now here are the most common answers to the test:

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

1. 5 cents
2. 5 minutes
3. 47 days

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You don’t know how the answer to the first question was 5 cents and not 10 cents? Still wondering how the second question lasted 5 minutes, not 100 minutes? Fortunately, Presh Talwalkar, author of The Joy of Game Theory: An Introduction to Strategic Thinking explained how to find the right answers on his blog, Pay attention to your decisions. If these explanations leave you with more questions than answers, you are on your own.

1. Suppose the ball costs X. Then the bat costs \$ 1 more, so it’s 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
2. If it takes 5 minutes for 5 machines to create 5 widgets, then it takes 5 minutes for 1 machine to create 1 widget (each machine makes a widget in 5 minutes). If we have 100 machines working together, each one can create a widget in 5 minutes. So there will be 100 widgets in 5 minutes.
3. Every FORWARD day, the patch doubles in size. So every BACKWARDS day means the patch size decreases by half. So, on day 47, the lake is half full.