"Now I know": Solving logical puzzles using graphs

It's not every day that a mathematics puzzle makes it into mainstream media. But that's what happened recently with "Cheryl's Birthday problem". This problem was posted by Kenneth Kong, the host of a Singaporean TV show, on his Facebook page on 10 April, and it went viral. Since then, the problem has appeared in such esteemed publications as the New York Times, the BBC and the Sydney Morning Herald.