When is Cheryl's birthday?

Hello people,

Last Friday, as I was just wrapping up my work at office and happily anticipating yet another weekend was when I found this interesting question -When is Cheryl's birthday - which was asked in a 5th grade exam for 10 year old in Singapore[!] - which later became the question for 14 year olds and then eventually the question which was asked in an Olympiad exam - and the news said it went viral.

So I was intrigued, naturally, and I looked it up. But as I had to get out of office quickly and catch by train home, all I could do was take a snapshot on my phone. I thought I had a 3 hour train journey and what better thing to do.

So this is the 'viral' question:

So, when is Cheryl's Birthday?

Now, I have figured it out this way, it would be great to know how you people thought it through, rather than the answer and the logic. To know the thought processes would be good. Hope you will share...


Thanks!