When is Cheryl’s birthday? Yes, this simple question went viral on social media after MediaCorp Channel 8 presenter Kenneth Kong on Facebook. Well, this is because it was the main question in the tricky math problem given during the Singapore and Asean Schools Math Olympiads (SASMO) on April 8, 2015. The contestants consist of Secondary 3 and 4 students, with ages 14-15 years old.
In case you are having a hard time viewing the photo above, below are the details of the problem and the correct answer as well. You can also try to solve it yourself before you scroll down this page.
Albert and Bernard just became friends with Cheryl, and they want to know when her birthday is. Cheryl gives them a list of 10 possible dates.
May 15 === May 16 === May 19 === June 17 === June 18
July 14 === July 16 === August 14 === August 15 === August 17
Cheryl then tells Albert and Bernard separately the month and the day of her birthday respectively.
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.
So when is Cheryl’s birthday?
Apparently, social media users had a debate with the correct solution and answer to this math problem. With different solutions and answers provided, SASMO Executive Director Henry Ong was kind enough to reveal the correct answer. Mr.Ong clarified that the difficult math question is #24 of the 25 questions of the contest.
According to Mr.Ong, around 28 000 students joined the contest this year. These kids came from Brunei, Bulgaria, Cambodia, China (including Hong Kong and Macau), Indonesia, Malaysia, Mongolia, Myanmar, Philippines, Singapore, Thailand, Vietnam, UK, and Uzbekistan.
Below is the official solution and answer.
Base on the explanation, 18 and 19 are mentioned once each, for June and May, respectively. We must note that both Albert and Bernard know the month or the day. With Bernard initially admitting that he doesn’t know Cheryl’s birthday, we can conclude both June and May are now ruled out.
And because only July and August are left, it is very much unlikely that the date is 14, 15, or 17 simply because these dates are mentioned in both months. On the third statement, Albert said he already know Cheryl’s birthday. This means that 16 is the remaining day that is not repeated in the other months.
Therefore, Cheryl’s birthday is July 16.
Did you have the same answer? 🙂
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