A question intended for math-savvy high school students in Singapore that stumped everyone on the internet has been solved.
Designed for 14 to 15-year-olds pupils in the Singapore and Asian Schools Math Olympiads, it quickly went viral as millions of people struggled to even start working it out, Stuff.co.nz reported.
Christchurch maths teacher Stephen McConnachie, who managed New Zealand’s own Math Olympiad team for three years, said problems such as the one that went viral were useful in challenging the negative stigma people often had towards math.
Singapore’s Ministry of Education told The Straits Times that the question was not part of the primary or secondary mathematics syllabus and not reflective of the type of questions set in its mathematics assessments.
Here is the problem, which has prodded the grey cells of people:
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 and 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 it either.
Bernard: At first I din’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?
Here’s the true “solution”, which emerged out of a debate in Singapore ‘s Study Room:
First, it’s important 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, it is known that Albert is certain that Bernard does not know the birthday, and 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 does not 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 July 16, August 15, or August 17 (not August 14 as then he can not know).
Since Albert subsequently can also be sure of the date, he must know it is July. If it is August, he cannot be sure, as there are two dates, August 15 and 17.
So the answer is July 16. (ANI)