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midterm 2014 Q2D

Posted: Mon Feb 13, 2017 9:55 pm
by Anna_Kim_2E
I am having a bit of confusion for sig figs when ln, e, or log is involved.

I am aware that for ln(X), if X has 3 signifiant digits then the value for ln(X) should have 3 decimal places.
But in midterm 2014 Q2D, e^4.63 = 102, which also means that ln(102) = 4.63. 4.63 has 2 decimal places.
Then, Shouldn't e^4.63 be equal to a value with 2 sig figs instead of 102 which has 3 sig fig?

Re: midterm 2014 Q2D

Posted: Mon Feb 13, 2017 11:44 pm
by Chem_Mod
Let's say X has 3 sig figs:

Ln(X) or Log(X) will then have 3 decimal places
eX or 10X will have 3 significant figures (not necessarily 3 decimal places)

Re: midterm 2014 Q2D

Posted: Tue Feb 14, 2017 7:13 pm
by Anna_Kim_2E
I am still having a bit of confusion.

So on the problem, on the attached picture, how is the sig fig of the answer determined? Do we just disregard the value that ln becomes? ln(12.90/7.60)