What Day is Cheryl's Birthday?

A problem from the Singapore Mathematical Olympiad has been travelling around the internet, since being shared on Facebook by Kenneth Kong. This site provides an easy way to work through the problem, to better understand the correct solution and how to solve the problem.

How to Use This Site

Click on one of the possible dates for Cheryl's birthday. Then you can follow the thoughts that Albert and Bernard have as they attempt to solve the problem. If one of the claims they make does not match up with the date you selected, then that claim will show up in red, and you can hover over it to see why it is incorrect.


Pick a possible day

Follow Albert and Bernard's Discussion

I don't know when Cheryl's birthday is, but I know that Bernard does not know too.

At first I don't know when Cheryl's birthday is, but I know now.

Then I also know when Cheryl's birthday is.