WASHINGTON – Got a few minutes to kill? Are you in the mood to feel like a fool? Then welcome to the logic problem, “Cheryl’s birthday.”
It’s a problem that Singapore TV host Kenneth Kong posted to Facebook as a test for students in a math Olympiad held earlier this month, CNN reports. (As you struggle with it, don’t think about the fact that this was designed for high-schoolers; you’ll just get more annoyed.)
So here it goes: Cheryl doesn’t want to tell her friends Albert and Bernard exactly what her birthday is, but she gives them a list of 10 dates, one of which is the real one. The dates are May 15, May 16, May 19, June 17, June 18, July 14, July 16, Aug. 14, Aug. 15 and Aug. 17. She then tells Albert which month her birthday is in; Bernard, the date.
Albert then tells Bernard, “I don’t know when Cheryl’s birthday is, but I know Bernard doesn’t know either.”
That’s all Bernard needs: He replies, “At first, I didn’t know when Cheryl’s birthday is, but I know now.”
And that tips Albert off: “Then I also know when Cheryl’s birthday is.”
It’s all about the process of elimination. The solution, which is embarrassingly simple once it’s pointed out to you by Georgia Tech mathematician Matt Baker, is below via CNN:
No word on whether Albert and Bernard were still friends with Cheryl after having to go through all that.
