Solving the Singapore Math Problem
As viral phenomena go, the math problem posted by Singaporean TV host Kenneth Kong is more interesting than the latest celebrity stupidities. It made people use their brains for a change. However, Kong claimed that this math problem is given to fifth graders. Nope, not even the vaunted Singaporean educational system dishes this out to fifth grade children. Turns out it’s a question in a high school math Olympiad.
Before I learned that it’s a mathlete problem, pride compelled me to prove to myself that I am smarter than a 10-year-old Singaporean (Sucker!). Time I should’ve spent writing my column, so now it is this week’s column.
1. The Problem
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 17Cheryl 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?
Read our column at InterAksyon.com.
Answers to questions you might be asking, unless you wandered onto this site purely by accident >>>
April 16th, 2015 at 15:39
Was going to try and solve the problem as well but found myself really bothered by how the problem didn’t state if Albert knew that Bernard was given the date and if Bernard knew that Albert was given the month. (Of course, it would be the correct assumption that each knew what the other had been given, based on the characters’ succeeding statements). But in a lot of these types of problems, what one knows and what one knows the other knows are often a part of the problem that it seemed quite an oversight not to indicate that yes, though they had been given their data of month and date respectively and separately, Cheryl indicated to them later on what type of information the other had been given.
And I found that particular piece of missing confirmation made the problem less mathematically elegant and potentially made the problem a lot more complicated:
“If Albert knew the month but wasn’t aware what particular data Bernard had been given, how could he have made the conclusion that Bernard didn’t know her birthday as well?”
Which would lead to the assumption of an assumption, that Albert would think that based on Cheryl’s enigmatic nature, Cheryl wouldn’t simply give Bernard some bit of data that would be useless in figuring out Cheryl’s birthday. But what if Albert supposes that Bernard might have been given some other type of data, such as: “not May” or “not August”. Alternately, Albert could’ve been a tiny bit of paranoid and think, “I was given the month, but what if Bernard had been given both month AND date?”
April 16th, 2015 at 19:02
noelz: Overthinking will not solve it. Only work with what you’re given.
It should be clear to a 5-year old that Albert knew Bernard had the day and Bernard knew Albert had the month.
Unless the problem you’re interested in is: How to get out of solving this problem. Also known as: Excuses.
April 16th, 2015 at 23:57
Ang sarap sabunutan ng Cheryl na yan, ha!