Three significant figures?

• lasagnia

  2 Oct 08, 17:27

  Hi All,

  On the cover page of the Mathematics papers, students are told that " if the answer is not exact, give the answer to three significant figures".  I like to clarify what the words in bold really mean.

   

  Let's say that the answers are 1016 or 24569 exactly, are the students to give those as the final answers?  Or must they round up the answers to three significant figures to 1020 and 24600 respectively?

   

  Thanks.
• Ferret

  2 Oct 08, 17:30

  "if the answer is not exact"

   

  if its exact, why bother ? 

• tr@nsp0rt_F3V3R

  2 Oct 08, 18:33

  APP. this is the O' levels rule, apply to phy, chem, A. math, E.math and maybe much more. this is how it goes,

  if 155/3, and is 51.6666666666666666666666666666666666666666666666

  you round off to 3 s.f., that is 51.7

  but if it is 2425008/3 =808336, leave it as it is, unless otherwise state.

  and  if 113/ 4 = 28.25 , a perfect nos., UNLESS it's SPA, pr ptherwise stated, it should be left the way ot is.

  but if u are taking e. maths, if i am not mistaken, leave it is fraction, improper of mixed number is a better choice... as far as possible

  also. note that an angle, if it's in a lot of dec. best is put in one D.P.

• wishboy

  3 Oct 08, 00:26

  for trigo questions, it's best to convert non-exact answers to 5 sf before converting to 3 sf to leave as final answer
  so for subsequent parts to the question, u can use the 5 sf values for more accurate answers

  i have a qn about money
  if the answer is non-exact, do we convert to 3 sf, or leave to 2 dp?

• Ahm97sic

  3 Oct 08, 09:27

  Hi Wishboy,

  For question on money, if the answer is not exact, we should round off to 2 decimal places eg 18.35892 should rounded off to $18.36.

  Another common mistake that students made on questions on money is if the answer is 21.2, some students will leave their answers as 21.2. However, this is not correct, the answer should be $21.20, otherwise marks will be deducted or worse in E. maths where the question is only 1 mark and "O" level examiner cannot give 1/2 mark, so the examiner will give the students zero mark in this case.

  Thank you for your kind attention.

  Regards,

  ahm97sic

• caleb_chiang

  3 Oct 08, 09:29

  it refers to decimals...

• FirePig

  4 Oct 08, 11:43

  If the answers is exact, dont change anything la. If the answer is not exact, then use 3 sig figures la.