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[Another]

Magma had always kept all the infinite tail in "a". The sum is there implicitly but only the result of the infinite sum is ever used explicitly.

[Skyrunner]

Mm, I think I see it now >_>

... This is probably why I won't be going into math <_<

[ed boy]

I think Magma is wrong.
His answer only had then rolling it once each, I think, while the problem said they kept rolling until one side won.

You only need to roll each time if you're summing the probability of getting it on your first go, second go, etc. If you consider the probability of winning on any of your goes all at once, you don't need to roll multiple times.

[Pnx]

Ah, thanks for answering my question guys. I honestly feel a little guilty for asking considering I could probably have figured it out on my own.

[MagmaMcFry]

Well, I recall that the way specified for it being done on this particular exam is:
-snop-

Would you get points off for doing it my way?

[MagmaMcFry]

From the looks of it, yes, though the person grading the exam could give discretionary marks to make up the difference.

So you get points off for being clever? Way to ruin maths.

[Scelly9]

PTW, because math.

[Soadreqm]

So you get points off for being clever? Way to ruin maths.

What you need to ask yourself is this: Are you trying to get points, or find the correct answer?

Let the grades fall where they will! Do it your way! BE FREE!

[MagmaMcFry]

So you get points off for being clever? Way to ruin maths.

What you need to ask yourself is this: Are you trying to get points, or find the correct answer?

Let the grades fall where they will! Do it your way! BE FREE!

When it's on an IB exam, the goal is points. Here's a sample mark scheme for the exam where that problem came from: make note of how they grade answers. They do allow alternate solutions not shown on the mark scheme, but it does have to show all appropriate work. They're not checking for answers, but understanding of concepts.

They're testing for specific terminology, specific methods and specific intermediate steps? That's absolutely horrible. If I'd write this test, I'd get all of the accuracy points but almost no method points. Hell, I'd probably even lose some reasoning points by reasoning around the specified "thinkpaths". Isn't it enough that they get the right answers? It's only fucking calculation, for god's sake. "Answer given in the question"? Are these people maybe fucking kidding me, and also a little stupid? Did the guys designing the tests ever ask a real mathematician for their opinions? Who the hell needs to know a vertical asymptote? Who the hell cares about vertical asymptotes? When was the last time a real mathematician even used the word "asymptote"? Most people who write those tests wouldn't know how to solve a single logical problem if their lives depended on it, and that's because logical problems are considered "less useful" than vertical asymptotes, and are therefore not tested. But the goddamn vertical asymptotes can only make sense if you have learned to recognize and apply sense, and if people could learn mathematics instead of this slurry of arbitrary definitions and "correct" methods of calculation, they wouldn't even need to learn all these stupid specific things like vertical asymptotes, because they could fucking invent ways to solve those problems WHILE WRITING THE FUCKING TESTS. INCOHERENTRAEG.

[Vector]

Dammit, Magma, that's so clean.  Nicely done.

[MagmaMcFry]

Dammit, Magma, that's so clean.  Nicely done.

*bows* Competitive problem-solving FTW.

[RedWarrior0]

Vertical asymptotes are boring, anyways.

[da_nang]

Pretty sure they don't take away points here for solving it differently as long as it's correct and the reasoning is mathematically sound and clear. The reasoning is usually more important than the answer.

Spoiler (click to show/hide)

They do love to mess with the grade distribution when the examiners fuck up, though. 

[lordnincompoop]

I take IB Math HL, and I can attest to the fact that this isn't necessarily true.

On every single test I've seen so far, almost every method mark has been implied - that means that as long as the answer is correct, the rest doesn't matter. The most notable exception I've seen so far is precisely just this: Probability. That's the reason I lost some marks there, because I tend to find answers intuitively instead of the methods they use. With vectors, for example, I don't think I've seen a single required method mark.

Obviously you need to show your method, because otherwise the examiners wouldn't know whether you grasped the concepts or not, but that goes for any curriculum out there.

Don't criticise something you don't know much about, and don't just blindly paraphrase Lockhart's Lament just because you think it sounds cool (facetious comment). Sure, there are some silly parts to IB Math HL right now, such as the curriculum having linear algebra but not matrices, but it's under constant revision and that will likely be solved by the time the class of 2015 or 2016 comes along.

[palsch]

One thing worth noting, although I don't know if it applies here; some papers these days are being marked digitally with individual questions being sent to each marker. So question 8)a) might be marked by one person and 8)b) by another. At least one paper I'm aware of allowed for marks if the student used a wrong answer from a previous part then didn't show the previous part to the marker.

If I were taking such tests these days I'd put emphasis on each answer being as complete and self contained as I could.