A complicated high school test question is sending adults across the world back to school.
A math problem intended for sophomores and juniors in Singapore has the Internet asking, “When is Cheryl’s birthday?”
To help students figure out the equation, you are given some vague clues.
In the question, Cheryl is giving clues to two of her friends about her birthday.
Cheryl gives them a list of 10 possible birthdays:
May 15 May 16 May 19
June 17 June 18
July 14 July 16
August 14 August 15 August 17
Cheryl tells Albert her birth month, and tells Bernard the day of her birthday.
Albert: I don’t know when Cheryl’s birthday is, but I know that Bernard does not know too.
Bernard: At first I don’t know when Cheryl’s birthday is, but I know now.
Albert: Then I also know when Cheryl’s birthday is.
School organizers say this is one of the more difficult questions on the test.
If you’re still stumped, BBC News broke it down and solved the puzzle below.