<p>For the AP Chemistry exam, is it customary to carry all operations out and then round after analyzing the sig figs or to break the calculation into the different operations and round in between?</p>
<p>Because my teacher does it one way some books do the other.</p>
<p>**EDIT: I just realized I posted 2 threads accidentally when I went to change the typo in the title.</p>
<p>My teacher tells our class to round at the very end. Three digit, he doesn't care about sig figs though otherwise your calculations would be really off if you rounded mid-way.</p>
<p>I've heard that NOT rounding in between can lose you AT MOST 1 point. However, I doubt this very much. Can someone confirm?</p>
<p>Typically, I round in between calculations because that's the way Zumdahl explains it. Actually, he tells us to do the exact opposite doesn't he? Well, since we present our answers to the AP graders, I don't think it really matters too much as long as you show your work.</p>
<p>Yeah, the policy I've adhered to is also to round at the very end to maintain the highest accuracy.</p>
<p>Hmm, it seems we have conflicting beliefs.</p>
<p>Snipez, are you saying Collegeboard wants us to round in between?</p>
<p>At the end.</p>
<p>When only multiplication/division is involved, it is perfectly acceptable (and preferred) to carry all the decimals in your calculator, then round at the end. (Look back to the original data to see how many sig figs to round to.)
The only time intermediate answers affect sig figs is when addtion/subtraction creates one of those oddball shortened numbers. (Ex 242.2-242.0=.2, i.e. 4 sig figs is reduced to 1 sig fig.)
There have been one or two MC questions that directly test sig figs and require you to properly account for the effect of addition/subtraction but they were on older tests if I recall. It rarely is an issue in a free response question.
College board grading policy specifies that the maximum deduction for sig figs is 1 point per question. (Getting the sig figs wrong in every part of the question is the same one point deduction as getting the sig figs wrong in only one part.)</p>
<p>.5^2 + .5^2 = .4</p>
<p>or</p>
<p>.5^2 + .5^2 = .5?</p>
<p>In the former I rounded in between, in the latter I rounded in the end. So on the MC, which answer is the correct one?</p>
<p>.5 </p>
<p>always round at the end... rounding at the end yields a more accurate answer. Personally, I just do calculations in one long sequence and if thats not possible I use the variable storage function.</p>
<p>1) By the rules most high school students are taught, rounding in between equals 0.6, not 0.4. (0.25+0.25= 0.3+0.3=0.6)
2) The preferred answer is 0.5. Rounding once introduces less error.
3) The college board questions aren't that subtle. Their MC question from 1994 follows
42. Mass of an empty container = 3.0 grams
Mass of the container plus the solid sample = 25.0 grams
Volume of the solid sample = 11.0 cubic centimeters
The data above were gathered in order to determine the density of an unknown solid. The density of the sample should be reported as
(A) 0.5 g/cm3
(B) 0.50 g/cm3
(C) 2.0 g/cm3
(D) 2.00 g/cm3
(E) 2.27 g/cm3
As you can see, the choice is between 2.0 and 2.00, which simply requires that you NOT blindly restrict you answer to 2 sig figs because of the 3.0 in the original data.</p>
<p>Actually even numbers stay even preceding a lone 5. Opposite for odds.</p>
<p>Absolutely correct about the evens/odds, but a lot of students are still taught the old rule about rounding 5's up. That's one reason college board isn't going structure a question that way - they're not trying to test your knowledge of rounding rules, but rather sig fig rules in the context of gathering lab data - thus the type of question asked in 1994.</p>
<p>I don't know if it's fair to call it the "old rule"</p>
<p>the GAAP uses that rounding method as far as I know...</p>
<p>I assume you mean Generally Accepted Accounting Practices. That's interesting - I wasn't aware of that. I was assuming that the more statistically correct method (even/odd method) was being taught more in high schools since Statistics has become a more common high school course, but that many schools still taught the "5's round up" method. Anyone out there willing to chime in with what your school teaches? (Not that this is related to AP Chem.)</p>
<p>Sure the GAAP uses that protocol, but last time I checked, accounting doesn't equal science. </p>
<p>Sciences use the even/odd method because of the uncertain digits. The rounding procedure allows for both odds/evens to be rounded if preceding a 5 without bias. So the idea is that overall, the rounding will produced 50/50 numbers preceding 5's rounded up and down.</p>
<p>I completely agree with the odd/even rule. This was the only way I was ever taught with rounding. Rounding up with .5 seems statistically awkward.</p>