ATAR Notes: Forum

VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Mathematical Methods CAS => Topic started by: whichkim on November 03, 2013, 06:41:43 pm

Title: How picky are examiners?
Post by: whichkim on November 03, 2013, 06:41:43 pm: Doing my practice exams, I realized that I'm a lot more into using fractions than decimals (in Exam 1). I find fractions a lot more easier to work with in terms of multiplying, dividing, etc, etc. However, when it comes to the answers, most of the papers have their answers in decimals instead! Does it really matter? If it does matter then, when do I know when to use fractions/decimals?

Thanks in advance!
Title: Re: How picky are examiners?
Post by: Damoz.G on November 03, 2013, 06:45:29 pm: If you're used to using fractions as opposed to decimals, then that's great! All answers should always be in exact values (fractions) for both Exam 1 and 2. If it states in the question to give your answer as a decimal, then that's the only time that you use decimals. If nothing is stated in the question, then exact values are required to get the full marks.

Well done! :)
Title: Re: How picky are examiners?
Post by: Zealous on November 03, 2013, 06:46:02 pm: Fractions are usually safer, but of course something like 1/40 can be expressed as 0.025 which will still be marked correct (you might end up with decimals like this on exam 1). For exam 2, only give a decimal approximation when asked to (for irrational numbers etc.).
Title: Re: How picky are examiners?
Post by: Professor Polonsky on November 03, 2013, 06:53:48 pm: As long as it's an exact answer, it can be given as a decimal. For example, 0.25 and $\frac{1}{4}$ are exactly the same. On the other hand though, please don't write 0.33 if the answer is a third. Given that you're used to fractions, you shouldn't have any trouble in exam 1. It might be easier to work with decimals in some cases, but that's completely a matter of personal preference.

As others have mentioned, in exam two, you may be asked to give a decimal approximation in place of an exact answer. In that case, you should of course give your final answer as a decimal.
Title: Re: How picky are examiners?
Post by: Twanny666 on November 03, 2013, 07:48:27 pm: My teacher, the head of Methods, says that in Exam 1 they are very picky...
Whilst in exam 2 they are extremely lenient.
Title: Re: How picky are examiners?
Post by: Damoz.G on November 03, 2013, 07:54:42 pm: As I mentioned in my previous, this is what the instructions say for Exam 1:

Quote
In all questions where a numerical answer is required an exact value must be given unless otherwise
specified.

So never leave your answer as a decimal (Even for probability). I have gone through the Examiner's Reports, and they do pin students who don't give exact values.

If you want to use decimals when nothing is stated in the question, then do so but your running at a risk of losing absolutely stupid marks for not reading the instructions. Always simplify your answer until you can't simplify any further.
Title: Re: How picky are examiners?
Post by: Lejn on November 03, 2013, 07:59:26 pm: Is that last part about simplification really right? I mean I've read in various examination reports that the answer is for example:

1/2*ln(4) or ln(2) or other equivalent answers.
Title: Re: How picky are examiners?
Post by: Damoz.G on November 03, 2013, 08:04:22 pm: Quote from: Lejn on November 03, 2013, 07:59:26 pm
Is that last part about simplification really right? I mean I've read in various examination reports that the answer is for example:

1/2*ln(4) or ln(2) or other equivalent answers.

Sorry, that bit was supposed to be for an Exam 2 situation (Probably should have made that clearer). :)

But for an Exam 1 situation, always simply the obvious. e.g. 2/4=1/2
For something a bit more complex like that, in an Exam 1 situation, just leave it, otherwise you run the risk of making a mistake.

I don't want to sound rude (so please don't take it that way), but you should know when to simplify an answer or to leave it as it is.
Title: Re: How picky are examiners?
Post by: Professor Polonsky on November 03, 2013, 08:15:44 pm: Quote from: Damoz. on November 03, 2013, 07:54:42 pm
As I mentioned in my previous, this is what the instructions say for Exam 1:

So never leave your answer as a decimal (Even for probability). I have gone through the Examiner's Reports, and they do pin students who don't give exact values.

If you want to use decimals when nothing is stated in the question, then do so but your running at a risk of losing absolutely stupid marks for not reading the instructions. Always simplify your answer until you can't simplify any further.
But 0.5 and 0.25 are exact answers.
Title: Re: How picky are examiners?
Post by: BigAl on November 03, 2013, 08:28:43 pm: Use fractions unless otherwise stated...Mathematicians love fractions although engineers love up to 3-4 decimal places...
Title: Re: How picky are examiners?
Post by: Damoz.G on November 03, 2013, 08:46:22 pm: Quote from: BigAl on November 03, 2013, 08:28:43 pm
Use fractions unless otherwise stated...Mathematicians love fractions although engineers love up to 3-4 decimal places...

Yeah exactly, its the safest way to go. :)
Title: Re: How picky are examiners?
Post by: whichkim on November 03, 2013, 08:54:38 pm: Cool. Thank you everyone for the great answers! :) I guess I'll stick with using fractions in all my answers for Exam 1. I'm quite worried about losing marks for small things, seeing that an A+ means only losing 1-2 marks in the exam. Eeek.

Good luck to all those doing the Methods exam!
Title: Re: How picky are examiners?
Post by: Damoz.G on November 03, 2013, 09:01:00 pm: Quote from: whichkim on November 03, 2013, 08:54:38 pm
Cool. Thank you everyone for the great answers! :) I guess I'll stick with using fractions in all my answers for Exam 1. I'm quite worried about losing marks for small things, seeing that an A+ means only losing 1-2 marks in the exam. Eeek.

Good luck to all those doing the Methods exam!

Exactly, I've got the same mentality as you. You can never get marked down for using fractions as an answer, unless it states "Give your answer to _ decimal places".
Title: Re: How picky are examiners?
Post by: Tasmania Jones on November 04, 2013, 10:05:30 pm: I'm not doing 3/4 methods this year, but just out of interest, if you wrote BOTH the exact answer and the decimal approximation, you will not get any marks taken off right?

e.g
*random working*
=1/3
=0.33

Thanks :)
Title: Re: How picky are examiners?
Post by: Scooby on November 04, 2013, 10:22:49 pm: Quote from: AEwing on November 04, 2013, 10:05:30 pm
I'm not doing 3/4 methods this year, but just out of interest, if you wrote BOTH the exact answer and the decimal approximation, you will not get any marks taken off right?

e.g
*random working*
=1/3
=0.33

Thanks :)

Nah, in this case, if the exact value is required, you'd lose the mark. If you've got both down chances are you're not gonna get the mark. Just follow what the question says. If it doesn't specify an accuracy in terms of decimal places, give an exact answer :)
Title: Re: How picky are examiners?
Post by: Tasmania Jones on November 04, 2013, 10:26:18 pm: Oh really? :o I didn't think they were that picky...
Thanks for the prompt reply though 8)
Title: Re: How picky are examiners?
Post by: Damoz.G on November 04, 2013, 11:09:33 pm: Quote from: AEwing on November 04, 2013, 10:26:18 pm
Oh really? :o I didn't think they were that picky...
Thanks for the prompt reply though 8)

Yeah, always use Exact Values unless otherwise stated to "Give your answer to __ decimal places".

1/3≠0.33 (Its 0.33 recurring).

So always leave your answer as an Exact Value. Personally, I prefer to stick with fractions, and then you can't go wrong. :)
Title: Re: How picky are examiners?
Post by: achre on November 04, 2013, 11:20:36 pm: log_e(x) or ln(x)?
Title: Re: How picky are examiners?
Post by: Damoz.G on November 04, 2013, 11:25:47 pm: Quote from: achre on November 04, 2013, 11:20:36 pm
log_e(x) or ln(x)?

Means the exact same thing, but usually I use log_e(x) to avoid the possibility of using copy/paste from CAS (Which sometimes loses marks if CAS syntax is used). :P
Title: Re: How picky are examiners?
Post by: b^3 on November 04, 2013, 11:31:54 pm: Quote from: Damoz. on November 04, 2013, 11:25:47 pm
Means the exact same thing, but usually I use log_e(x) to avoid the possibility of using copy/paste from CAS (Which sometimes loses marks if CAS syntax is used). :P
$\ln(x)$ isn't cas syntax, $\ln(x)$ is the proper maths way of writing it (well they're both proper maths ways, I mean in actual maths it's convention to use $\ln(x)$ . With that being said, we've heard that apparently vcaa doesn't like $\ln(x)$ , so it's better to stick with $\log_{e}(x)$ (I'm not sure if you'd actually lose any marks or not if you didn't though).

Really some years they'll be more picker than others. If it is an easy exam, then to separate people they'll be more picky, and if it's a hard exam, they may be a little bit more lax. Before the group of teachers and such that get to go mark the exam, they have a big meeting and agree on how they're going to mark it which can change each year depending on what the head assessor decides.
Title: Re: How picky are examiners?
Post by: Damoz.G on November 04, 2013, 11:40:15 pm: Quote from: b^3 on November 04, 2013, 11:31:54 pm
$\ln(x)$ isn't cas syntax, $\ln(x)$ is the proper maths way of writing it (well they're both proper maths ways, I mean in actual maths it's convention to use $\ln(x)$ . With that being said, we've heard that apparently vcaa doesn't like $\ln(x)$ , so it's better to stick with $\log_{e}(x)$ (I'm not sure if you'd actually lose any marks or not if you didn't though).

Really some years they'll be more picker than others. If it is an easy exam, then to separate people they'll be more picky, and if it's a hard exam, they may be a little bit more lax. Before the group of teachers and such that get to go mark the exam, they have a big meeting and agree on how they're going to mark it which can change each year depending on what the head assessor decides.

I know its not CAS Syntax, but I just avoid it. :)
Title: Re: How picky are examiners?
Post by: BigAl on November 05, 2013, 06:59:38 pm: Quote from: achre on November 04, 2013, 11:20:36 pm
log_e(x) or ln(x)?
Well I'm lazy and I've been using ln(x) all the time..it's not a problem at all. I've seen couple of people using exp(x) instead of e^x at uni...also meteorologists love i,j,k hat although I use a tilde for vector notation :) so it's totally your choice
Title: Re: How picky are examiners?
Post by: BubbleWrapMan on November 05, 2013, 08:22:45 pm: Quote from: AEwing on November 04, 2013, 10:05:30 pm
I'm not doing 3/4 methods this year, but just out of interest, if you wrote BOTH the exact answer and the decimal approximation, you will not get any marks taken off right?

e.g
*random working*
=1/3
=0.33

Thanks :)

They go by whatever you give as your final answer. So if you wrote that they'd probably take a mark off (unless they wanted the two decimals).

Just give an exact answer unless asked otherwise.
Title: Re: How picky are examiners?
Post by: Tasmania Jones on November 05, 2013, 09:39:00 pm: Quote from: Timmeh on November 05, 2013, 08:22:45 pm
They go by whatever you give as your final answer. So if you wrote that they'd probably take a mark off (unless they wanted the two decimals).

Just give an exact answer unless asked otherwise.

Ah okay thanks :D