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Homework Help: Significant figures/rounding what the heck.

  1. Dec 16, 2006 #1
    Didn't use the template because it didn't make sense to do so for my question..

    Simple question here regarding significant figures. I am working through a textbook and in the answer section they often seem to round off to odd numbers which makes no sense to me. I decided to ignore it at first because I am so sure that I am doing it correctly, I mean... I learned to round in grade 2 :rolleyes: . But it seems to happen a lot and I figure that the person writing the text wasn't an idiot so...

    for [tex]\frac{1.20kg}{2.99x10^{-26}kg}[/tex] they have their answer as [tex]4.02x10^{25}[/tex]. I say that its [tex]4.01x10^{25}[/tex]

    Who's right? and why if I am not right.
    Last edited: Dec 16, 2006
  2. jcsd
  3. Dec 16, 2006 #2


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    Homework Helper

    According to my TI-83, you're right. Why is this bugging you? It's irrelevant. They often make mistakes, since writing down solutions on back pages of books isn't a very exciting and caution-keeping job. :wink:
  4. Dec 16, 2006 #3
    Okay, I thought I was losing my mind or something. lol
    Last edited: Dec 16, 2006
  5. Dec 16, 2006 #4
    I definitely agree that it is pretty insignificant, but it was happening like 1/5th of the time so it started to bug me.
  6. Dec 16, 2006 #5


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    Staff Emeritus
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    You have to remember that significant figures are a heuristic device that usually approximates a reasonable estimate of error.

    As such, there really isn't a "right" answer, and there are several different approaches to it. For example, "round to the nearest even number" is not terribly infrequent.
  7. Dec 16, 2006 #6
    Yes. Just remember that with rounding to Sig. Figs, that as long as your answer is realitively close to the correct answer, it's correct. I mean, most times you wouldn't get the same answer, but just make sure yours is around it.
  8. Dec 16, 2006 #7
    Alright great. Thanks :)
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