Singapore usually comes top (or nearly top) of the international rankings in primary maths performance. And when you read this confusing question – you can see why. It’s a brilliant logical puzzle, which will stump most adults.
At first glance, this question appears like a standard logic question that we all encountered during our time at school. But if you actually sit down and try to complete it, there’s a fair chance that you’ll soon be tearing your hair out.
The brain-twisting question went viral after it was posted by Singapore TV, presented Kenneth Kong on his Facebook page. He’s since revealed that the question was in fact set for 14-year-olds in the Singapore and Asean Math Olympiads, but it hasn’t stopped people from trying to tackle it.
This mind-boggling maths puzzle will twist your mind. Here’s the question in full…
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?
If you’re still unsure, the geniuses at Singapore’s Study Room have apparently worked out the answer, so here it is, courtesy of them.
Here’s the answer to the brain-twisting maths puzzle designed to 14-year-olds in Singapore that left the world confused!
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 July 16.
I think the more important question is whether Cheryl deserves a birthday gift at all after putting us through all of this.
