Sig fig question

[Xylitol]

Does a number like 345+/-15 have 3 or 2 sig figs? I'm not quite sure since 345 is 3 sig figs, but the uncertainty of 15 spans both the 10's and 1's digits.

 

[shortylickens]

2

3.45 x 10 to the 2

 

[Xylitol]

2

3.45 x 10 to the 2

but 3.45*10^2 is 3 sig figs lol. i'm just a little sketched out by the uncertainty of +/-15

 

[jaedaliu]

I'd say 2. the number is in a range from 3.3 to 3.5. So there's no detail in the ones unit. I'm sure someone that's taking k-12 math right now has a more complete answer.

 

[disappoint]

The number 345 is 3 sig figs

All non zero digits are significant.

 

[disappoint]

• All non-zero digits are considered significant. For example, 91 has two significant figures (9 and 1), while 123.45 has five significant figures (1, 2, 3, 4 and 5).
• Zeros appearing anywhere between two non-zero digits are significant. Example: 101.1203 has seven significant figures: 1, 0, 1, 1, 2, 0 and 3.
• Leading zeros are not significant. For example, 0.00052 has two significant figures: 5 and 2.
• Trailing zeros in a number containing a decimal point are significant. For example, 12.2300 has six significant figures: 1, 2, 2, 3, 0 and 0. The number 0.000122300 still has only six significant figures (the zeros before the 1 are not significant). In addition, 120.00 has five significant figures since it has three trailing zeros. This convention clarifies the precision of such numbers; for example, if a measurement precise to four decimal places (0.0001) is given as 12.23 then it might be understood that only two decimal places of precision are available. Stating the result as 12.2300 makes clear that it is precise to four decimal places (in this case, six significant figures).

http://en.wikipedia.org/wiki/Significant_figures

 

[Possessed Freak]

345 is 3 significant figures. With the error thrown in, the 5 is no longer significant (as far as I know). I would go with 2.

 

[disappoint]

345 is 3 significant figures. With the error thrown in, the 5 is no longer significant (as far as I know). I would go with 2.

What? This is incorrect. The 5 is significant even with the error thrown in. All trailing zeros are significant. Have you not even read this thread?

345 +-15 is 3 significant figures.

 

[jaedaliu]

What? This is incorrect. The 5 is significant even with the error thrown in. All trailing zeros are significant. Have you not even read this thread?

345 +-15 is 3 significant figures.

What? that is incorrect. The 5 is insigificant with the error thrown in. There is no trailing zero with the uncertainty. Did you even read the wiki page you linked?

345+-15 is equivalent to 345 +-4.3% so it's more than 1 and less than 2 significant figures. Which I believe convention would prefer you round to 2.

 

[disappoint]

I posted too hastily, I didn't see this:

Alternatively, the uncertainty can be stated separately and explicitly with a plus-minus sign, as in 20 000 ± 1%, so that significant-figures rules do not apply.

What that is saying is sig. fig. rules do not apply. The uncertainty is given.

 

[gururu2]

Don't confuse sig figures with decimal places. Your value cannot have a greater accuracy than your precision has.

340+/- 20 (2 sig figs)
300 +/- 20 (1 sig fig)
325.183 +/-0.001 (6 sig figs)
345 +/- 20 (incorrect) >> 350 +/- 20
345 +/- 15 (3 sig figs)

 

[JTsyo]

I posted too hastily, I didn't see this:
What that is saying is sig. fig. rules do not apply. The uncertainty is given.

that makes sense. If you know your error no need to rely on sig fig.