It involves one simple question, but the answers to this quick brainteaser are apparent to only four per cent of people - are you one of them?
Based on a 1963 study by Peter Wason, who devised one of the most famous tasks in the study of deductive reasoning, this brainteaser works to reveal how logical your thinking is.
Posted to YouTube, this version of the puzzle consists of four cards and two rules.
1. Cards have letters on one side and numbers on the other.
2. If a card has a vowel on one side, it must have an even number on the reverse.
Following the above, participants are asked which card(s) must be turned over to establish if the rule has been followed.
So, if you were given the cards A, K, 2, and 7, which ones would you turn over?
If you chose A and 7, you are correct.
But if you picked A and 2, you're incorrect, along with 46 per cent of people who took part in the original study.
Here's why A and 7 were the correct cards to turn over:
To establish whether or not the rule has been followed, you have to see if any of the cards don't follow the rule.