Can you solve the rogue submarine riddle? Difficulty level: Master - Alex Rosenthal
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“Bernard: I know whether you know whether I know whether you know whether I know whether you know whether I know whether you know whether I know whether you know whether I know whether you know whether I know whether you know my number.Albert: I don’t know your number."
But be warned…these are really difficult!
Generally speaking, logic puzzles attempt to bridge the gap between often complicated theorems and fictional scenarios to engage a variety of thinkers in deep mathematical and philosophical inquiry. Logician, mathematician, and creator of Alice’s Adventures in Wonderland, Lewis Carroll, introduced these riddles to the general public in 1887 in his book The Game of Logic. For a brief history of logic puzzles and several famous problems to work through yourself, check out this article from Mathigon. For a more in-depth exposition on mathematical logic, see this entry in the Stanford Encyclopedia of Philosophy, which includes a bibliography for further reading.
The sum and product puzzle presented in this “Submarine Riddle” is a type of ignorance problem (also known as a dynamic epistemic logic problem) in which one or more parties makes an ambiguous statement that reveals key information to the reader, allowing them to eliminate possible answers and arrive at a solution. In 2015, another example of an ignorance problem went viral after TV host Kenneth Kong posted a photo of the logic puzzle on social media. Created by Dr. Joseph Yeo Boon Wooi of Singapore's National Institute of Education, Cheryl’s Birthday Puzzle quickly swept the internet, with more than 5,000 shares in a matter of days. Several follow-up puzzles appeared soon after the original “Cheryl’s Birthday” riddle, including “Cheryl’s Age” and “Denise's Revenge.”
Want more riddles? TED-Ed has lots of fun and challenging brainteasers in our Riddles Series.
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