When Is Cheryl’s Birthday? Singapore Math Problem Turned World Phenomenon Solved!

Apr 15, 2015 at 12:40 pm |

The world was not ready yesterday when what was pitched as a middle school math problem from Singapore turned into a viral logic sensation.

While we almost had another dress situation, many people from around the world took this opportunity to put their rusty high school math skills back to work. But was that really the way to solve this problem?

The Problem:

In its original wording:

Clearly, the Singaporeans should be more concerned about their English than their math, but that’s beside the point. The bizarre wording and incorrect grammar of this problem only add to the mystery, however, and might just be the cause behind why so many people were stumped.

Long story short, Albert and Bernard want to know Cheryl’s birthday, so she gives them a list of 10 possible dates. She tells Albert the correct month and Bernard the correct day. Here’s where things get a little tricky: Albert (month) says that he doesn’t know her birthday, but he DOES know that Bernard can’t possibly know either.

To this, Bernard (day) responds that, thanks to Albert’s statement, he has figured out the correct day.

Knowing that Bernard has figured out the date, Albert is then able to deduce the correct date as well.


Were you able to solve the problem? Are Albert and Bernard schoolmates or creepy old men hitting on Cheryl at a bar? And, regardless, why is Cheryl so annoying?

If you need a hint to get started, consider drawing a quick chart with all the dates written out (visuals always help me). Secondly, think about fixing the wording, which might just be the trickiest part of all (the New York Times had a great rewrite).

Your final hint is that this is more of a logic issue than a “math problem” as originally described.

Stumped? Click to the next page to see the solution!

Were you able to solve the logic problem that took the world by storm?