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    (Source: REVISE EDEXCEL GCSE Statistics Revision Guide)

    Hello,

    Please, can you help me solve this question about the mean, variance and standard deviation:

    You have to use: √Σx²/n - (Σx/n)²

    The question is, the number of visits (x) to a dentist was recorded over 10 days.
    Σx = 200
    Σx² = 480
    Work out the mean, the variance and the standard deviation.

    Thanks
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    (Original post by sunflowerlion)
    (Source: REVISE EDEXCEL GCSE Statistics Revision Guide)

    Hello,

    Please, can you help me solve this question about the mean, variance and standard deviation:

    You have to use: √Σx²/n - (Σx/n)²

    The question is, the number of visits (x) to a dentist was recorded over 10 days.
    Σx = 200
    Σx² = 480
    Work out the mean, the variance and the standard deviation.

    Thanks
    It's recorded over 10 days so n is 10. You've been given Σx and Σx² and just sub these into the equations for mean, variance and standard deviation.
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    When I try to do that, it comes up with an error. I don't think I'm typing it in right.
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    (Original post by sunflowerlion)
    When I try to do that, it comes up with an error. I don't think I'm typing it in right.
    Are those numbers definitely correct? I tried subbing it in and i I got math error as well so I can only think the values are wrong.
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    (Original post by miless090)
    Are those numbers definitely correct? I tried subbing it in and i I got math error as well so I can only think the values are wrong.
    Yeah they are. I've just checked answers in back:
    Mean = 20
    Variance = 80
    Standard deviation = 8.9
    But I have no idea how they got that, there's no workings.


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    The numbers can't be right- you can't square root a negative! The book might have made a typo- if you use Σx² = 4800 then you get the right standard deviation and variance
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    (Original post by somegirlcalledea)
    The numbers can't be right- you can't square root a negative! The book might have made a typo- if you use Σx² = 4800 then you get the right standard deviation and variance
    Thanks a lot There was a typo in the book.


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