S'pore math question on students' birthday months has everyone stumped. Again.

4 - 3 = 1

Mandy How | February 14, 2018, 04:59 PM

Singapore's academic scene is known for its nigh-impossible mathematics questions.

Like Cheryl's birthday:

And a few more that will leave you struggling:

Now, a new question has popped up on the scene:

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Quick math

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In case you can't see it, the question reads:

"There are 37 students in a class. How many students, at the least, are born in the same month?"

Commenters on the post suggested a few possible answers that range from zero to four, and then a mind-boggling 26:

[related_story]

"Congruence arithmetics":

Someone decided to calculate how many would have the same birthday month "at most":

And this one is... ??

And this one, which might just be our favourite response:

We ask people who can actually math

Because we are noobs who can't figure out an answer, we consulted with a few folks who actually know what they're doing.

The first is Kevin Huang, a math teacher who specialises in upper primary heuristics.

Huang believes the question is ambiguously phrased, and that it should be asking for the least amount of students that have to be picked before you can be sure that at least two of them have the same birthday month.

In this case, for him, the answer is 13, and students will have to know apply the worst case scenario method. 

This is the method he used:

You pick one student and assume that his birthday falls in January. 

In the worst case scenario, the next 11 students you pick will have birthdays in each of the other 11 months.

Only the 13th student will end up in the same month as one of the previous students.

Therefore, the answer is 13.

Huang also gave us this table to illustrate his theory:

However, if we were to follow the original phrasing of the question, the immediate answer would be two, according to him.

An approach that a mathematics degree holder we also asked agrees with. He analysed it as a logic question rather than, say, one that requires probability:

Assume that 0 students are born in the same month. This will mean that all students are born in different months, which is impossible because there are only 12 months but 37 students. 

Assume that one student is born in the same month. That wouldn't make sense and it would be grammatically wrong.

Assume that two students are born in the same month — it makes sense. And it's possible. Cos there are more than two students.

Continue with the assumptions that three, four, ..., 37 students are born in the same month — all of which are possible. 

However, going back to the question of how many students, at the least, are born in the same month, the answer would be two.

So maybe it isn't actually that difficult after all.

But if the question was intended to stir confusion and go viral, it has done its job well, we suppose.

 

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