Adding and Subtracting Significant Figures

  • Thread starter cvc121
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  • #1
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Homework Statement


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!

Homework Equations




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.
 

Answers and Replies

  • #2
phinds
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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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