A TV presenter in Singapore is behind an unlikely viral sensation after he posted a math problem that was asked to the country’s 14-year-old children.
The students were participating in the Singapore and Asian Schools Math Olympiads (SASMO).
Initially, the problem sounds confusing as hell. Which is why you start to question your own intelligence compared to that of a 14-year-old.
But in the end, it’s actually kind of easy.
See if you can figure it out:
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?
Stumped?
Here’s the ‘solution’, courtesy of a debate on Singapore’s Study Room:
First we need to figure out if Albert knows the month or the day. If he knows the day, then there is no chance that Bernard knows the birthday, so it must be that Albert knows the month.
From the first statement, we know that Albert is sure that Bernard doesn’t know the birthday, so May and June should be ruled out (the day 19 only appears in May and the day 18 only appears in June). In other words, if Albert had May or June, then he cannot be sure that Bernard doesn’t know, since Bernard could have had 18 or 19.
Following that statement, Bernard knows that May and June are ruled out.
Then, Bernard is able to know which month it is. So it must be either July 16, August 15 and August 17 (not 14th as then he can’t know).
Since Albert subsequently can also be sure of the date, he must know it’s July. If it’s August, he can’t be sure as there is August 15 and 17.
So the answer is ______
But you knew that already, right?
Photo Credit: Justin Lewis -Getty Images
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