Am I the only one that does this?

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Discussion Overview

The discussion revolves around the practices and quirks of rounding numbers in calculations, particularly in the context of significant figures and decimal places. Participants share their personal habits, preferences, and the reasoning behind their approaches to rounding in both intermediate and final answers.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants express a tendency to write down many decimal places until reaching a digit below 5, citing indecision or laziness in rounding.
  • Others argue that anything beyond two decimal places is excessive and may be misleading.
  • Several participants mention specific rounding habits, such as looking for certain digits (0, 1, 9) or using a specific number of significant figures based on the inputs.
  • There are differing opinions on the treatment of intermediate values versus final answers, with some advocating for keeping intermediate results unrounded in calculators.
  • Concerns are raised about misunderstandings of significant figures among students, particularly regarding the implications of decimal places on accuracy.
  • Participants share humorous takes on rounding constants like e and the use of assumed values in engineering calculations.

Areas of Agreement / Disagreement

Participants generally express a variety of personal rounding practices, with no clear consensus on the best approach. Disagreement exists regarding the appropriateness of rounding in different contexts, particularly between intermediate and final answers.

Contextual Notes

Some participants highlight the confusion surrounding significant figures and the implications of rounding, indicating that their understanding evolved through practical experience rather than formal education.

1MileCrash
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When I get an answer in my calculator, I write down all of the decimal places until I get to one that is below 5 because I'm too lazy/indecisive to actually pick a place to round and do it.

I'm talking 6 or 7 places sometimes.

I can't be the only one?
 
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Yes, You are some kind of weirdo.:-p
Anything more than two decimals is usually lying.
 
Concurrence. Weirdo. :biggrin:
 
Not only do I do that, if the 5 comes too soon (within 5-8 digits), I will continue on to the next 5. No idea why I do this. Intermediate values, oh wow, I save 20 places sometimes...
 
QuarkCharmer said:
No idea why I do this.
It is merely a quirk, Quark.
 
I always seek the double 3's.
 
Anything more than 2 decimals is a no go in my books :P
 
I take off points for insignificant digits.
 
There are no insignificant digits in my math. Usually it's pure until the answer pops out in terms of pi. Then I can take the decimal place as far as I like. This isn't physics.

Usually I look for a 0, 1, or 9. Those are my happy number rounding places.
 
  • #10
As a rule of the thumb, I usually use as many significant digits as the question has.
 
  • #11
If it's the final answer to a question, it should be rounded to whatever number of sig figs is appropriate for the initial input numbers.

If it's an intermediate answer, it should stay in your calculator (that's what your calculator's memory is for) and not be written down at all, unless your question asks you to show that answer also. In that case you should round off the written version appropriately, but use the unrounded version in the calculator for further calculations.
 
  • #12
I round [itex]e[/itex] to 3. Is that bad?
 
  • #13
Not as bad as rounding it to 4.
 
  • #14
Dembadon said:
I round [itex]e[/itex] to 3. Is that bad?

No joke, my physics professor usually uses 10 for g when working examples.
 
  • #15
Dembadon said:
I round [itex]e[/itex] to 3. Is that bad?

Vanadium 50 said:
Not as bad as rounding it to 4.

Gentlemen! We have a winnar!
 
  • #16
Vanadium 50 said:
I take off points for insignificant digits.
As an engineer, I have too many assumed values in my calcs for sig figs to matter.
 
  • #17
Vanadium 50 said:
I take off points for insignificant digits.

And this is basically how I stopped the habit in my undergrad
 
  • #18
jtbell said:
If it's the final answer to a question, it should be rounded to whatever number of sig figs is appropriate for the initial input numbers.

See, my problems are exact. It's not until the final calculation that things get decimal-ized.
 
  • #19
I don't do it for final answers, because then its just wrong, its assuming a known value for values that aren't known (or equivalently, assuming that all decimal places after the given measurement are zeros)

You will find it surprising how many students at the college level don't know the reasoning behind significant figures and think that more decimal places means a more accurate answer.

1.3 meters is not 1.30 meters, it means we stopped measuring after a tenth of a meter.

I never learned that concept in school when I learned about significant figures. It only came to me when actually doing lab work.
 
  • #20
1MileCrash said:
1.3 meters is not 1.30 meters, it means we stopped measuring after a tenth of a meter.

I never learned that concept in school when I learned about significant figures. It only came to me when actually doing lab work.

I did learn that. My most confusing times currently are when I get to the end of a probability question and the final move turns out an enormous fraction which practically requires a decimal conversion to be useful comparatively. How far do I take it? As far as I like is my guess. So, that's to a 0, 1, or 9.
 
  • #21
1MileCrash said:
I don't do it for final answers, because then its just wrong, its assuming a known value for values that aren't known (or equivalently, assuming that all decimal places after the given measurement are zeros)

You will find it surprising how many students at the college level don't know the reasoning behind significant figures and think that more decimal places means a more accurate answer.

1.3 meters is not 1.30 meters, it means we stopped measuring after a tenth of a meter.

I never learned that concept in school when I learned about significant figures. It only came to me when actually doing lab work.

A corollary to that observation: some people think a reading is more accurate if the instrument display is digital :biggrin:.
 
  • #22
However, seeing hundreds of cases where the average of 30 integers between 0 -10 are cut to one digit, maybe we are loosing a wee bit of information. On the other hand, none of my kids has 2,184736 children. It's not doable. :-p
 
  • #23
ArcanaNoir said:
See, my problems are exact. It's not until the final calculation that things get decimal-ized.

Wait, wait. Let's get our terminology correct, here. Murdering a perfectly good symbol is decimation. :biggrin:
 

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