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Adding and Subtracting Significant Figures

  1. Oct 4, 2016 #1
    1. The problem statement, all variables and given/known data
    Hi,

    To add or subtract sig figs, it is to my understanding that the answer is reported so that it reflects the least precise number.

    For the example 43.4 - 22 - 3, would I report my answer as 18 or 20?
    Thanks. Any help is very much appreciated!

    2. Relevant equations


    3. The attempt at a solution
    The least precise number is 3 but I am not sure if I would report my answer with 1 or 2 sig figs. I am guessing that my answer should be 20 since it has only one significant figure as well.
     
  2. jcsd
  3. Oct 5, 2016 #2

    phinds

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    Gold Member
    2016 Award

    Been a long time since I did such a thing formally but as I recall the normal practice is to say that your error is the RMS of the individual errors, which in this case would be sqrt((.05*2 + .5*2 + .5*2)/3) = .7 so your answer is 18.4 +/- .7
     
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