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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: dekoyl on November 07, 2009, 10:03:12 pm

Title: Rounding off during working out
Post by: dekoyl on November 07, 2009, 10:03:12 pm: I know this has been asked before but I can't find it using the search function.

Anyway, during a 4 mark question, do we round off each part of the question to obtain the final part of the answer?

There's a question that requires you to find the mole but the mole comes out to be 133 333. The final answer needs to be rounded off to 3 sig figs but I used 133 333 to find the final answer whereas VCAA used $1.33 \times 10^{5}$ . Anyway, their final answer was $5.63 \times 10^7$ whereas mine was $6.01 \times 10^7$ so there is quite a bit of difference.
Title: Re: Rounding off during working out
Post by: TrueTears on November 07, 2009, 10:18:44 pm: I'd definitely put $1.33 \times 10^5$

But for the calculation for later parts I'd use $133 333$ then round off to however many sig figs/d.p's they want.
Title: Re: Rounding off during working out
Post by: hyperblade01 on November 07, 2009, 10:19:12 pm: Teacher emailed VCAA ages ago for mid-years - they said to quote to sig figs for each part but carry the exact value in your calculator as you go through the question

I was also told that they take both unrounded and rounded - but you never know...
Title: Re: Rounding off during working out
Post by: silva on November 07, 2009, 10:20:49 pm: Quote from: TrueTears on November 07, 2009, 10:18:44 pm
I'd definitely put $1.33 \times 10^5$

But for the calculation for later parts I'd use $133 333$ then round off to however many sig figs/d.p's they want.
but thats not what VCAA do in their solutions? so do we do their method and use the rounded off figure for each answer
Title: Re: Rounding off during working out
Post by: TrueTears on November 07, 2009, 10:21:34 pm: Quote from: silva on November 07, 2009, 10:20:49 pm
Quote from: TrueTears on November 07, 2009, 10:18:44 pm
I'd definitely put $1.33 \times 10^5$

But for the calculation for later parts I'd use $133 333$ then round off to however many sig figs/d.p's they want.
but thats not what VCAA do in their solutions? so do we do their method and use the rounded off figure for each answer
I assume it's the same for maths (asked in another thread), they'd take both answers, rounded and unrounded like hyperblade said.
Title: Re: Rounding off during working out
Post by: dekoyl on November 07, 2009, 10:22:03 pm: Ah okay. Cause this is what they did:
(http://i38.tinypic.com/65wz8p.png)
Title: Re: Rounding off during working out
Post by: kendraaaaa on November 07, 2009, 10:25:27 pm: I put sig figs on the paper in each step but leave it unrounded in the calculator.
Title: Re: Rounding off during working out
Post by: shinny on November 07, 2009, 10:26:53 pm: Every company cbfs with doing things properly including VCAA themselves it seems, but it's been suggested by VCAA many times to carry it over through an entire question. To emphasise this point however, you're probably best to write something like n(CO2) in the next question to quote the exact value, rather than writing down the approximated one whilst using the exact value on your calculator to avoid confusing the examiner on how you got such a number in the end, since it wouldn't add up properly. Otherwise, sometimes I just wrote down a few more sig figs than was required from the previous question in the following question to show that I'm using the exact value.
Title: Re: Rounding off during working out
Post by: silva on November 07, 2009, 10:32:43 pm: Quote from: shinny on November 07, 2009, 10:26:53 pm
Every company cbfs with doing things properly including VCAA themselves it seems, but it's been suggested by VCAA many times to carry it over through an entire question. To emphasise this point however, you're probably best to write something like n(CO2) in the next question to quote the exact value, rather than writing down the approximated one whilst using the exact value on your calculator to avoid confusing the examiner on how you got such a number in the end, since it wouldn't add up properly. Otherwise, sometimes I just wrote down a few more sig figs than was required from the previous question in the following question to show that I'm using the exact value.

that is so confusing that VCAA do that then (round off their answers) as it suggests to us that we should do the same and carry it on through our answers whereas they want us to use the value in our calculator..very lazy on their behalf and fkn confusing
Title: Re: Rounding off during working out
Post by: Collin Li on November 07, 2009, 10:39:32 pm: Quote from: kendraaaaa on November 07, 2009, 10:25:27 pm
I put sig figs on the paper in each step but leave it unrounded in the calculator.

Same

Quote from: shinny on November 07, 2009, 10:26:53 pm
Every company cbfs with doing things properly including VCAA themselves it seems, but it's been suggested by VCAA many times to carry it over through an entire question. To emphasise this point however, you're probably best to write something like n(CO2) in the next question to quote the exact value, rather than writing down the approximated one whilst using the exact value on your calculator to avoid confusing the examiner on how you got such a number in the end, since it wouldn't add up properly. Otherwise, sometimes I just wrote down a few more sig figs than was required from the previous question in the following question to show that I'm using the exact value.

Completely true +1, and smart idea about including more sig-figs in intermediate steps to "explain" to the examiner what you're doing. I do things like this too, but not for sig-figs.