Mathematics SL; exact answers vs. 3 significant digits.

[y.v]

For the SL Mathematics exam, let's say I get an answer of 312390 for a question.

Should I round it off to 3 significant figures i.e. 312000 or let it be?

Also, let's say that the question involves time or money.

Then, is it better to give your answer in 3 significant figures or are you required to convert it into __ hours __ minutes or __ years __ months or __dollars __cents ... ?

Edited May 2, 2009 by y.v

[Eyas]

To answer the latter question first, always use 3sf and the same unit given in the question. I.e. for a compound interest question where the initial investment is given in dollars, (unless told otherwise in the body of the question), the answer should be in dollars, rounded to 3 significant figures. Same for time.

Usually though for money questions, you are asked to give you answer to two decimal places (I've seen most past paper questions like that when solving money questions).

As for the first question, you need to always use 3 significant figures unless told otherwise. If you get something like 312390, I usually like to write the final answer as "312390 =(approx_ 312000 (3 s. f.)". That shows 312000 as the final answer and shows the examiner that it is approximated.

[sweet]

3sf. our teacher always tells us to

Edited May 4, 2009 by sweet

[Hedron123]

You will only have to round answers in Paper 2 as, for paper 1, you get simple numbers that can be calculated mentally. Rounding is always to 3 significant figures unless otherwise stated. Anyway, they can only deduct 1 point in the whole paper for not rounding answers (although it is 1 point, it's not thaaaat much). G'luck!

[Vvi]

For time, I don't convert my answer into hours and minutes. The markscheme allowes you to leave it as 14.2 hours, because then I suppose rounding seconds becomes problematic.