Significant Figures?

Question

I am having trouble rounding the answers i get from a problem using significant figures. What is good a way I can remember how to do it? Please give examples for addition, subtraction, multiplication, and division WITH as many decimal places as you want and please give GOOD descriptions. Thanks!

Answer 1

Favorite Answer

whether it is addition, subtraction, multiplication or division:

use the figures the problem gives you to use and when you get the answer based on those figures then round up or down according to the problem's requirement for the number of significant figures.

0.00273 has 3 significant figures

27,300 has 3 significant figures

20,703 has 5 significant figures

rule of rounding - once you decide what place you are going to round to: ...150000... > x ...249999... rounds to ...2

anything equal to or greater than ...150000... rounds up to ...2 and anything equal to or less than ...249999... rounds down to ...2

so

123456789 round to 3 significant figures is 123000000

123456789 round to 4 significant figures is 123500000

123456789 round to 5 significant figures is 123460000

987654321 round to 6 significant figures is 987654000

0.0087654 round to 3 significant figures is 0.00877

0.0012345 round to 3 significant figures is 0.00123