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A257087 Based on "Cheryl's Birthday" problem. 0
515, 516, 519, 617, 618, 714, 716, 814, 815, 817 (list; graph; refs; listen; history; text; internal format)



This sequence is based on a logic problem that appeared on a math olympiad test in Singapore and became famous via Internet news. The problem is as follows.

Cheryl tells her friends Albert and Bernard that her birthday can be represented by one of the three-digit numbers in this list (where the first digit represents the month and the last two digits represent the day). She then secretly tells Albert the first digit (the month) and she tells Bernard the final two digits (the day). Albert and Bernard then have the following conversation:

Albert: "I don't know when Cheryl's birthday is, but I do know that Bernard also does not know."

Bernard: "At first I didn't know Cheryl's birthday, but now I do."

Albert: "Then I now also know when Cheryl's birthday is."

The goal of the puzzle is to determine Cheryl's birthday based on the given information.


Table of n, a(n) for n=1..10.

Kenneth Chang, A Math Problem From Singapore Goes Viral: When Is Cheryl's Birthday?, The New York Times, Apr 15 2015.

Kenneth Kong, Facebook Post. [Date?]

Ed Mazza, Here's the answer to the Cheryl's birthday math problem., Huffpost, Apr 15 2015.


517 is interpreted as May 17 and 814 is interpreted as August 14.


Sequence in context: A228999 A168126 A246244 * A254643 A322883 A332151

Adjacent sequences:  A257084 A257085 A257086 * A257088 A257089 A257090




Tom Edgar, Apr 16 2015



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Last modified October 4 21:22 EDT 2022. Contains 357240 sequences. (Running on oeis4.)