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Homework Help: Sig figs ! Help

  1. Sep 7, 2012 #1
    ok so this may sound really dumb but i need to refresh my memory on this so here is the question

    6.941+63.996+35.45 = 106.387

    how do i know how many sig figs to round too with this?
  2. jcsd
  3. Sep 7, 2012 #2


    Staff: Mentor

    Since the 35.45 is not written as 35.450 then you have to use it as the limiting significant figures hence your answer would be 106.39
  4. Sep 7, 2012 #3
    so you always use the smallest one correct?
  5. Sep 7, 2012 #4


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    Gold Member

    Consider this: Say you are doing an experiment and you know one parameter to a good degree of precision and another parameter to a lesser degree of precision. Now say we have some other parameter that is dependent on these two parameters. When you combine them (i.e by dividing, multiplying etc) this dependent parameter will be affected by this parameter which you knew to a lesser precision. Hence, yes, you should quote your final result to the lowest number of sig fig in your data.
  6. Sep 7, 2012 #5


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    Staff: Mentor

    This is not exactly true.

    100.23 + 0.11 = 100.34


    100.23*0.11 = 11

    Rules for addition and subtraction are slightly different than for multiplication and division.

    Don't worry too much about significant figures. There are much better ways of expressing precision of the result. Sigfigs are more of a rule of thumb.
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