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Math Help - significant figures

  1. #1
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    significant figures

    how many sig. figs. are in the number : 2400


    the book says 2, and this calculator says 4:

    http://www.chem4free.info/calculators/signdig.htm


    ??
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  2. #2
    Super Member Matt Westwood's Avatar
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    Read what it says in the link:

    "Trailing zeros in large integers are always counted by this script. An example will make this clear. The number 545100 shall be written in scientific notation

    with six significant digits as 5.45100e5
    with five significant digits as 5.4510e5
    with four significant digits as 5.451e5

    If it is written as 545100 then it is impossible to know how many significant digits there are in it. This script counts all trailing zeros if you do not use scientific notation."

    It is not possible to know whether the 00 in the 2400 are genuinely zeroes, as they would be if the actual number is, for example, 2400.123 or whether they have been rounded off from, for example, 2419.622.

    So both are "correct" and the question is undecidable without further information.

    Mind, your teacher probably wants you to give the answer 2 and will mark you down if you say 4 no matter how loudly you call him a fascist.
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  3. #3
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    Quote Originally Posted by Matt Westwood View Post
    Read what it says in the link:

    "Trailing zeros in large integers are always counted by this script. An example will make this clear. The number 545100 shall be written in scientific notation

    with six significant digits as 5.45100e5
    with five significant digits as 5.4510e5
    with four significant digits as 5.451e5

    If it is written as 545100 then it is impossible to know how many significant digits there are in it. This script counts all trailing zeros if you do not use scientific notation."

    It is not possible to know whether the 00 in the 2400 are genuinely zeroes, as they would be if the actual number is, for example, 2400.123 or whether they have been rounded off from, for example, 2419.622.

    So both are "correct" and the question is undecidable without further information.

    Mind, your teacher probably wants you to give the answer 2 and will mark you down if you say 4 no matter how loudly you call him a fascist.

    hm its 2? ok.. thats kind of hard to fathom, but ok i ll go with 2.
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  4. #4
    Super Member Matt Westwood's Avatar
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    why would it be hard to fathom? Zeroes are considered in this context not to be "significant figures", they are just placeholders. 2400 means 2 thousand (the first s.f.) and 4 hundred (the second s.f) and nothing else.

    We do not know without further information whether the zeroes in the number are "significant" in that they genuinely "signify" that this digit is not 1, 2, 3 etc. We don't know whether the number has been rounded from something with different digits in the tens and / or units place and we *can't* know without the context being made clear.

    Which is why this is a terminally stupid question and should never have been asked. Burn the maths book it came out of and throw the ashes into the teacher's face.
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  5. #5
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    Quote Originally Posted by Matt Westwood View Post
    why would it be hard to fathom? Zeroes are considered in this context not to be "significant figures", they are just placeholders. 2400 means 2 thousand (the first s.f.) and 4 hundred (the second s.f) and nothing else.

    We do not know without further information whether the zeroes in the number are "significant" in that they genuinely "signify" that this digit is not 1, 2, 3 etc. We don't know whether the number has been rounded from something with different digits in the tens and / or units place and we *can't* know without the context being made clear.

    Which is why this is a terminally stupid question and should never have been asked. Burn the maths book it came out of and throw the ashes into the teacher's face.
    hm yah i see your point. thanks for the help man.
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