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    I tried to calculate the variance for the following question on a casio calculator fx-85gt:
    number absent: 0 1 2 3 4 5
    number of days: 54 24 11 4 2 1
    and i got 1.06 even though the answer is 1.13
    I was wondering if anyone else is getting this value on their calculator as well and if you know where I might be going wrong?

    Thank you!
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    What do you have for \sum x and \sum x^2?
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    (Original post by DFranklin)
    What do you have for \sum x and \sum x^2?
    15 and 55 respectively
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    (Original post by Stanspam)
    15 and 55 respectively
    OK, to be honest I don't think I know how Casio's do this well enough (my knowledge is quite a few years out of date).

    I was expecting \sum x to be

    0 * 54 + 1 * 24 + 2 * 11 + 3 * 4 + 4 * 2 + 5 * 1 = 71.

    and \sum x^2 to be

    0 * 54 + 1 * 24 + 4 * 11 + 9 * 4 + 16 * 2 + 25 * 1 = 473.

    You can then find E[x] and E[x^2] and the the variance.

    Edit: I remember there being a particular way you were supposed to indicate you had multiple values (so you could enter 54 sets of 0 without entering "0" 54 times, but not the details. I'm guessing that's where you've gone wrong, but it's only a guess.
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    (Original post by Stanspam)
    I tried to calculate the variance for the following question on a casio calculator fx-85gt:
    number absent: 0 1 2 3 4 5
    number of days: 54 24 11 4 2 1
    and i got 1.06 even though the answer is 1.13
    I was wondering if anyone else is getting this value on their calculator as well and if you know where I might be going wrong?

    Thank you!
    Your calculator has given you the standard deviation. You need to square it to get the variance.


    (Original post by DFranklin)
    I was expecting \sum x to be

    0 * 54 + 1 * 24 + 2 * 11 + 3 * 4 + 4 * 2 + 5 * 1 = 71.

    and \sum x^2 to be

    0 * 54 + 1 * 24 + 4 * 11 + 9 * 4 + 16 * 2 + 25 * 1 = 473.
    I agree with your \sum x, but I think that your \sum x^2 should be 161, not 473. (That's the trouble with stats, numerical slips are so easy to make.
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    (Original post by Pangol)
    Your calculator has given you the standard deviation. You need to square it to get the variance.




    I agree with your \sum x, but I think that your \sum x^2 should be 161, not 473. (That's the trouble with stats, numerical slips are so easy to make.
    Meh, that's an error in the spreadsheet I used (and fixed, and then put the old wrong value in here, anyhow).

    Thanks, anyway! (Also, good spot on his answer being the s.d.)
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    (Original post by Pangol)
    Your calculator has given you the standard deviation. You need to square it to get the variance.




    I agree with your \sum x, but I think that your \sum x^2 should be 161, not 473. (That's the trouble with stats, numerical slips are so easy to make.
    But both the variance and standard deviation are being given as 1.06 by the calculator

    And square rooting answer gives 1.03 instead of 1.13
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    (Original post by Stanspam)
    But both the variance and standard deviation are being given as 1.06 by the calculator
    I expect that you are looking at the population and sample versions of the standard deviation. They are both standard deviations. You need to square them to get the variance.
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    (Original post by Pangol)
    I expect that you are looking at the population and sample versions of the standard deviation. They are both standard deviations. You need to square them to get the variance.
    but squaring these values still produces the wrong answer?
    Is there perhaps a different way you achieved the answer using the stats mode on the calculator?
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    (Original post by Stanspam)
    but squaring these values still produces the wrong answer?
    Is there perhaps a different way you achieved the answer using the stats mode on the calculator?
    When I square either of the standard deviations that the calculator gives us (and I agree with your value), I get the variance you say that you need.
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    (Original post by Pangol)
    When I square either of the standard deviations that the calculator gives us (and I agree with your value), I get the variance you say that you need.
    Thank you so much, I got the answer!

    Do you know why I have to square separately for grouped data though, since this step isn't necessary for data that isn't grouped?
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    (Original post by Stanspam)
    Thank you so much, I got the answer!

    Do you know why I have to square separately for grouped data though, since this step isn't necessary for data that isn't grouped?
    Without knowing the calculator details, I think you're wrong. I'm pretty sure the calculator always gives you the standard deviation and not the variance.

    I'd guess the most likely reason you need to square here is because it's asking for the variance, and previous questions where you haven't need to have asked for the standard deviation.
 
 
 
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