BBC maths quiz

Phil_aka_Pip

Not sure I agree with the method of solving question 4, seems like its the long way round. I wrote the expression as (4 + 9/15) - (2+ 5/15) to get 2 + 4/15. But they wanted you to multiply up the non fractional parts as well. I had to do that to get the numbers in the form required to answer the question (I did get 7/7 by the way), but is there something I'm missing here? 

chillidoggy

FFS, it's Friday night: curry and piss in the Chilli household. I can't see straight, never mind all that, Phil!

Sporky

Any danger of a link?

snakemanStoo

Is there the possibility that they wanted it resolving to fractions of 15ths so that is was obvious what you were subtracting?

then you'd get 69/15 - 35/15 = 34/15 = 2 + 4/15

Phil_aka_Pip

Questions: http://www.bbc.co.uk/news/magazine-23779549

Their answers http://news.bbc.co.uk/1/shared/bsp/hi/pdfs/22_08_13_maths_questions.pdf 

I think it would be pretty damning to get any of them wrong, but I was curious about the working for Q4

Phil_aka_Pip

snakemanStoo said:

Is there the possibility that they wanted it resolving to fractions of 15ths so that is was obvious what you were subtracting?

then you'd get 69/15 - 35/15 = 34/15 = 2 + 4/15

well yes that's what I had to do in then end to get it in the right form. just struck me as the long way round though

Phil_aka_Pip

chillidoggy said:

FFS, it's Friday night: curry and piss in the Chilli household. I can't see straight, never mind all that, Phil!

sorry @chillidoggy I'm having a detox weekend !

snakemanStoo

I was taught to make it obvious what you were doing in order that on a question worth multiple marks you'd still score marks for correct method and "correct" working out you'd still score marks, rather than just leaping in with the (maybe) wring answer.

Not that I did, I just got it right to the annoyance of a maths teacher who thought I was lazy and irritating just because I was lazy and irritating.

Really, true story.

digitalscream

Why did you even bother? The answers were all 2 4/15 - all they were really asking you to do is convert 2 4/15 into a top-heavy fraction.

Phil_aka_Pip

digitalscream said:

Why did you even bother? The answers were all 2 4/15 - all they were really asking you to do is convert 2 4/15 into a top-heavy fraction.

you had to do the working to select the right answer. I still say my original method is more efficient 

digitalscream

Phil_aka_Pip said:

digitalscream said:

Why did you even bother? The answers were all 2 4/15 - all they were really asking you to do is convert 2 4/15 into a top-heavy fraction.

you had to do the working to select the right answer. I still say my original method is more efficient 

You don't have to do your working - you have to explain how you got the answer. The logical train of thought (all answers are 2 4/15, therefore the question is which is the correct representation) would still get you the full marks in any exam.

Of course, multiple-choice exams never ask you for your working, so it's irrelevant anyway

EDIT: It's also a bit of a test of your exam-taking skills. Nowhere does it ask you to show your working (on the page or in the test). It just asks you for the answer. The PDF is just to show how the answers could be worked out. Doing it your way would simply waste time, when you can arrive at the correct answer in a couple of seconds and move on to the next question...

Phil_aka_Pip

digitalscream said:

Phil_aka_Pip said:

digitalscream said:

Why did you even bother? The answers were all 2 4/15 - all they were really asking you to do is convert 2 4/15 into a top-heavy fraction.

you had to do the working to select the right answer. I still say my original method is more efficient 

You don't have to do your working - you have to explain how you got the answer. The logical train of thought (all answers are 2 4/15, therefore the question is which is the correct representation) would still get you the full marks in any exam.

Of course, multiple-choice exams never ask you for your working, so it's irrelevant anyway

this was a multiple choice of 3 workings. you had to do the working to select the working which was the same as you'd got. my query was why you would multiply up the integers rather than just subtract the 2 from the 4 and deal with the fractional parts separately

digitalscream

Phil_aka_Pip said:

this was a multiple choice of 3 workings. you had to do the working to select the working which was the same as you'd got. my query was why you would multiply up the integers rather than just subtract the 2 from the 4 and deal with the fractional parts separately

No, it's not; none of them are workings at all, they're simply statements (two of which are false and one is true). One of them is a top-heavy fraction which equals 2 4/15, the other two are not. It's far simpler than your method, because all you have to do is work out the numerator (which is the only difference between the three statements):

(2 * 15) + 4

As I said, done in about 2 seconds.

Your query is irrelevant, because it's simply not the quickest way to arrive at the correct answer; getting to 2 4/15 is silly, because you're already given that part. In multiple-choice questions, the possible answers form a valuable part of the question itself especially in cases like this.

It's fine if you don't believe me, but I can pretty much guarantee that I've taken more maths exams than most people on the forum and this is exactly how we were taught to do it (and it served me very well)

Phil_aka_Pip

You seem insistent on misunderstanding me! yes I can see that 2 4/15 is the answer. we're given it and we can evaluate the expression to get it if we can be bothered. The "statements" (only one of which is correct) are things you get when you try to evaluate the original given expression. (if you don't like me calling them "workings" then please forgive me but they look like intermediate stages in the evaluation which is why I gave them that name). But they assume a method which is (to me) the long way round. And its the method I'm asking the question about, not the answer. Why would you multiply up the integral parts when you can deal with them separately as integers and then you've only got the originally given fractional parts to worry about? 

digitalscream

Phil_aka_Pip said:

You seem insistent on misunderstanding me!

Not really - at least, not the original question, which was "Not sure I agree with the method of solving question 4, seems like its the long way round". I was simply saying that I don't agree with your method or the one given in the PDF, because the answers imply that the question itself is a red herring and therefore any attempt to evaluate the original expression is just generating extra work for yourself and therefore not the most efficient way of doing it...and certainly a silly thing to do in an exam (which is the context for these questions).

However....

Phil_aka_Pip said:

Why would you multiply up the integral parts when you can deal with them separately as integers and then you've only got the originally given fractional parts to worry about? 

Aside from the fact that this seems to me like "which of these long-winded ways of doing it is the least long-winded"...your way still involves a conversion to top-heavy fractions, so it's not really much heavier in terms of operations. Something I observed during my extended stay in maths classes is that some people deal with single, large numbers better and others (such as you) prefer to deal with numbers with multiple parts. In short, whatever you're most comfortable with.

viz

Why have you had to take so many maths exams, DS?

digitalscream

viz said:

Why have you had to take so many maths exams, DS?

GCSE, A/O level, A-level, further maths A-level and a maths degree involving 12 exams per year

(not counting the 3 Open University module exams I took as a kid 'cos the 'rents mistakenly thought I was some sort of maths prodigy...I bloody hated maths then, and I still do...)

viz

Ah, so not retaking your o'level 3 dozen times like I had to (which is 48, I believe). If you hate maths so much, I hope you don't go and get a job in it with that pesky maths degree of yours!

digitalscream

viz said:

Ah, so not retaking your o'level 3 dozen times like I had to (which is 48, I believe). If you hate maths so much, I hope you don't go and get a job in it with that pesky maths degree of yours!

I'm a computer programmer, which - despite the stereotype - has not required me to use anything from my degree at all (although it'd be rather cool to revisit the module I did on encryption, the subtext of which was "this is how to break it").

In fact, the only time I got close was a mini-dissertation I had to do as part of a job application, which amounted to reverse-engineering a simplified form of Google's distributed data storage mechanism. I only applied for the job because I enjoyed the challenge and I wanted to see if I got the answer right

Phil_aka_Pip

digitalscream said:

Phil_aka_Pip said:

You seem insistent on misunderstanding me!

Not really - at least, not the original question, which was "Not sure I agree with the method of solving question 4, seems like its the long way round". I was simply saying that I don't agree with your method or the one given in the PDF, because the answers imply that the question itself is a red herring and therefore any attempt to evaluate the original expression is just generating extra work for yourself and therefore not the most efficient way of doing it...and certainly a silly thing to do in an exam (which is the context for these questions).

However....

Phil_aka_Pip said:

Why would you multiply up the integral parts when you can deal with them separately as integers and then you've only got the originally given fractional parts to worry about? 

Aside from the fact that this seems to me like "which of these long-winded ways of doing it is the least long-winded"...your way still involves a conversion to top-heavy fractions, so it's not really much heavier in terms of operations. Something I observed during my extended stay in maths classes is that some people deal with single, large numbers better and others (such as you) prefer to deal with numbers with multiple parts. In short, whatever you're most comfortable with.

Thank you. I guess I didn't express myself properly to start with.

EDIT on the subject of How to do multiple choice questions under exam conditions, the most efficient method would seem to be (as you imply) to eliminate those choices which are obviously wrong. BUT: it looks to me as if they were trying to test your understanding of how to evaluate quantities which are expressed as fractions with different denominators. So assuming that you can handle such things an alternative might be to evaluate the expression and see which of the proffered "intermediate stages" matches what you've got. That's what I did (rightly or wrongly) - I have to admit here that I don't ever remember getting multiple choice questions in a maths exam. If you didn't understand how to handle this kind of arithmetic but you were capable of eliminating the obviously wrong choices, then you'd have got your points for a right answer without understanding what the question was about. So I'm not sure it was a good question. Unlike Q1, where you needed to know the answer was 3.4cos(72) and without that knowledge you'd have only scored by a lucky guess.