Singapore Math Question Guardian Cheryl

The Singapore Maths Question-Answer

Smarter than a 14-year-old?

Jump to the answer.

Among The Guardian‘s articles from today you can find this very intriguing maths problem.

Initially thought to be part of a test for schoolchildren, the answer to the question created a lot of amazement at how brilliant people from Singapore are, given that children are able to solve something that even adults struggle with.

Nevertheless, an update of The Guardian’s article revealed that the problem in question is in fact part of a Maths Olympiad for the best 40 percent of Singaporean 14-15-year-olds. Still impressive!

The Guardian Singapore Maths question – the logic behind the answer

Working out the answer.
Working out the answer.

Now, how can we tackle the problem at hand? We know that:

  • Albert is told the Month: could be May, June, July or August
  • Bernard is told the Day: could be 14, 15, 16, 17, 18, 19

After they are told the month and the day respectively, Albert cannot know the birthday, but he is certain that neither does Bernard. That means that the month he was told was under no circumstances May or June, which are the months that could allow Bernard a chance to know the birthday from the start, seeing as they contain unique dates: May 19th and June 18th. So we now know that:

  • Albert is told the Month: either July or August
  • Bernard is told the Day: either 14, 15, 16 or 17

Once Bernard hears what Albert has to say, he can deduce the month, which is either July or August. Afterwards, he says he knows the birthday, which removes 14 out of the equation, since 14 can be found in both July and August. So the possibilities left are: July 16th, August 15th or August 17th. All of these dates work for Bernard, but the key information that helps us identify the right answer is the fact that Albert also knows the answer at the end, after Bernard does. If he does know without a doubt, August is out of the question, as it has two possibilities: either the 15th or the 17th. So the only date left is July 16th.

The correct answer is therefore July 16th. If you have something to add, feel free to comment!

 

Ioana Toader.

 UPDATE:

The author of The Guardian article that brought this maths question to our attention has also posted his reasoning together with the answer, and whaddyaknow? It really is July 16th! It’s so unbelievable that in the comments people still argue that either June 17th or August 17th is correct by simply making inferences out of nowhere. Remember: this is a logic puzzle, not a telenovela scenario where people lie and blurt out things impulsively!

 

Ioana Toader

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