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Math Help - Significant Figures and Rounding

  1. #1
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    Significant Figures and Rounding

    Hello,
    Recently I have encountered a problem in which I was to figure out how many seconds I was in class each week. My class is 0.833 hours long and we meet three times a week. I came up with 8,996.4 seconds. I need to round this to three significant figures because there are 3 in the information provided in the question (correct?) but everything rounds up and I would have 9,000...which is not 3 significant figures. Help please?
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  2. #2
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    Re: Significant Figures and Rounding

    Quote Originally Posted by Phillipians314 View Post
    Hello,
    Recently I have encountered a problem in which I was to figure out how many seconds I was in class each week. My class is 0.833 hours long and we meet three times a week. I came up with 8,996.4 seconds. I need to round this to three significant figures because there are 3 in the information provided in the question (correct?) but everything rounds up and I would have 9,000...which is not 3 significant figures. Help please?
    Round you answer to 9000 and then give it as 9.00 \times 10^3
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  3. #3
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    Re: Significant Figures and Rounding

    Hello, Phillipians314!

    Recently I have encountered a problem in which
    I was to figure out how many seconds I was in class each week.
    My class is 0.833 hours long ?? and we meet three times a week.
    I came up with 8,996.4 seconds.
    I need to round this to three significant figures
    because there are 3 in the information provided in the question (correct?).
    But everything rounds up and I would have 9,000 ... which is not 3 significant figures.
    Help please.

    First of all, why did you write the length of your class as a fraction of an hour?
    . . And then try to convert hours into seconds?

    If your class is 50 minutes long,
    . . then it is: . 50 \times 60 \,=\,3000 seconds per meeting.

    With three meetings per week,
    . . you spend: 3 \times 3000 \,=\,9000 seconds per week.


    The answer is accurate to three significant figures: .9000

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  4. #4
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    Re: Significant Figures and Rounding

    Quote Originally Posted by Soroban View Post
    Hello, Phillipians314!


    First of all, why did you write the length of your class as a fraction of an hour?
    . . And then try to convert hours into seconds?

    If your class is 50 minutes long,
    . . then it is: . 50 \times 60 \,=\,3000 seconds per meeting.

    With three meetings per week,
    . . you spend: 3 \times 3000 \,=\,9000 seconds per week.


    The answer is accurate to three significant figures: .9000
    I have to disagree with your answer, Soroban. Trailing zeroes are never significant unless they come after a decimal point.
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  5. #5
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    Re: Significant Figures and Rounding

    I'm going to jump into this and say that the number of significant figures is ambiguous for "0"s. I won't say, like mr fantastic, that "trailing zeros are never significant" (emphasis mine) but certainly you need to write 9.000 \times 10^3 in order that the number of significant figures not be ambiguous.
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