Goddamn Sig Figs!

[liuetenant]

JUst to recap, how do we all do significant figures again???

if it's a multi step question, do we use the round off answer or the asnwer in the calculator?

the thing is, i jsut did VCAA 2009 Q10, and they used the rounded off answer to calculate the final mass....whereas i did not and used the calculator answer...safe to say they got 0.19mg, whilst mine was 0.2mg..so would i be wrong? :O

any help is much appreciated!

[Laith]

that is the same answer except yours is one sig fig over their's (watch your sig figs)

[liuetenant]

so what would i do? used the rounded answer from the prevous question to work out my subsequent question like they did? or use my unrounded answer?

[Triazic]

I didn't make this, but it's good shit.


a + b = c: (or -)
c is rounded to the least number of decimal places of a or b:
Eg: 20.21 + 1.22 = 21.43 and 21.23 + 6.2 = 27.4

a x b = c: (or /)
this is the one most people are familiar with; c is rounded to least number of sig figs of a or b 
Eg: 12.0 x 4.00 = 48.0

a^b = c:
If b has x decimal places, c is rounded to x sig figs:
Eg 10^1.24 = 17. (the . is there for a reason, it signifies that both the 1 and the 7 are significant)

NB: If you're wide awake you would wonder what would happen if you get something like 4^3 or 10^5, with no decimal places; I did some experimenting and worked out that it's best to leave it as 10^x: so 4^3 = 10^2 ("no" significant figures) and 10^5 = 10^5. Try it out for yourself if you don't believe me.

log(base a) b = c
If b has y sig figs, then c is rounded to y decimal places:

Eg: [H+] = 0.00100 M => pH = -log(10)0.00100 = 3.000

[banditkeith]

Always use the numbers in your calculator.
Example, if you got 4.5463405 in your calculator and the information given is to 3 sig figs then
you write down 4.55 on the paper but leave the 4.5463405 in the calculator to be used for the
next calculation

[liuetenant]

alriteo, that helps. thanks!