Sig Figs at the Beginning or End
Moderators: Chem_Mod, Chem_Admin
Sig Figs at the Beginning or End
If a question requires many calculations (addition/subtraction AND multiplication/division) then at what point are you supposed to follow the sig fig rules? Do you base it on the given numbers or do you do it at each step before reaching the answer?

 Posts: 50
 Joined: Thu Jul 25, 2019 12:16 am
Re: Sig Figs at the Beginning or End
I would apply the sig fig rules at the point where you reach the answer so it keeps your calculations accurate. If you round after every step, it would throw off the numbers slightly. I base the sig fig rules based on the given numbers depending on what's being calculated and keep in mind which value has the least sig figs.
Re: Sig Figs at the Beginning or End
I actually think that once you've applied multiplication to something that you've added/subtracted, you have to use sig figs rather than the rules for addition/subtraction. If you were to multiply something first and then add, you'd follow the addition/subtraction rules.
I guess the way I think about this is that when we determine how many decimal places for addition/subtraction, you're striving for the most accurate possible answer. So, the most decimal places would be the most accurate because you already have precise values, and you now want to follow the most precise previous value.
I guess the way I think about this is that when we determine how many decimal places for addition/subtraction, you're striving for the most accurate possible answer. So, the most decimal places would be the most accurate because you already have precise values, and you now want to follow the most precise previous value.

 Posts: 100
 Joined: Fri Aug 30, 2019 12:16 am
Re: Sig Figs at the Beginning or End
Like Karyn said, I would just wait to round to the correct sig figs after doing all the calculations. Usually the amount of sig figs depends on the least amount that is provided in the question. If you're using addition/subtraction and multiplication/division, then you base it off the rules for multiplication and division.

 Posts: 13
 Joined: Sat Aug 03, 2019 12:15 am
Re: Sig Figs at the Beginning or End
The point is to stay really close to the number you got by rounding, in the early stages of the problem. Dr. Lavelle briefly mentioned in class. The number being divided determines sig figs in answer.

 Posts: 5
 Joined: Wed Sep 18, 2019 12:22 am
Re: Sig Figs at the Beginning or End
If there's multiple addition/subtraction and multiplication/division steps, I try to keep a higher number of sig figs than what I need for the problem. So if the final answers need 2, I might try to keep 4 sig figs so that way, when I go through all the math, the final answer won't be rounded too much up or down. It's about what's realistic for you to use in your calculator/what decimal point your calculator goes to and deciding how many sig figs is enough to prevent rounding errors, since with a final answer that only needs 2 sig figs, you don't need to keep 6 in every step of your calculations.

 Posts: 184
 Joined: Wed Sep 18, 2019 12:18 am
Re: Sig Figs at the Beginning or End
AT THE END! Do your best to keep as many figures as possible throughout your work. One way I do this if I do the problem on paper is writing an excess amount of figures (usually at least 3 more sig figs than needed) and then using that number in the next calculation. Once you get the final answer, round to the necessary sig figs.

 Posts: 64
 Joined: Wed Sep 18, 2019 12:18 am
Re: Sig Figs at the Beginning or End
My TA said to use as many decimals as possible throughout the problem and calculations, and then only do Sig Figs for the final answer.

 Posts: 128
 Joined: Sat Sep 07, 2019 12:16 am
Re: Sig Figs at the Beginning or End
As everyone said, round the final answer to the correct number of sig figs as given in the question.
To add on, if you want to be super precise and also avoid typing in a dozen decimals over and over, you can save numbers in your calculator (on some models).
To add on, if you want to be super precise and also avoid typing in a dozen decimals over and over, you can save numbers in your calculator (on some models).

 Posts: 108
 Joined: Wed Feb 20, 2019 12:17 am
Re: Sig Figs at the Beginning or End
As said above, you shouldn't convert to sig figs till the end so storing in your calculator as you go is very helpful. You can generally assign values to a letter so you can call it back later. For example, on the TI30X, once you have a value you click "STO" and select a a letter to assign to that value and click "enter". To use it later, click "2nd" then "STO" and select the letter corresponding to the value you want!

 Posts: 58
 Joined: Thu Jul 25, 2019 12:17 am
Re: Sig Figs at the Beginning or End
If the problem requires many calculations and steps, I would end each step with more significant figures than necessary just to avoid any error. At the very end, round your final answer to how many ever significant figures are necessary. I think this is crucial because even rounding slightly up or down in the middle of calculations could affect the end result.

 Posts: 101
 Joined: Fri Aug 30, 2019 12:17 am
Re: Sig Figs at the Beginning or End
You want your answer to be as accurate as possible so definitely focus on significant figures at the end of your calculation. In most cases, you could get away with rounding Oxygen's atomic mass to 16 grams or Hydrogen to 1.01 grams, but essentially you want to keep those significant figures and round your final answer based on the significant figures of the numbers given in the original problem.

 Posts: 102
 Joined: Thu Jul 25, 2019 12:16 am
Re: Sig Figs at the Beginning or End
Round to your sig figs at the very end of calculating; if you do it at the very beginning, your calculations will steadily grow more and more inaccurate because of all the rounding errors that compounded on each other. I like to keep really high amounts of precision with my early calculations so I can prevent any of those annoying rounding inaccuracies.
Re: Sig Figs at the Beginning or End
It's best to apply the sig fig rules at the end of all calculations so you get the most accurate answer :)

 Posts: 102
 Joined: Wed Sep 18, 2019 12:18 am
Re: Sig Figs at the Beginning or End
All calculations should be done while keeping as many sig figs as possible (or as many as your calculator allows). Then, when you round at the end, you can be confident that your final rounded answer is as accurate as possible.
Return to “Significant Figures”
Who is online
Users browsing this forum: No registered users and 2 guests