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Math Help - Statistic Help

  1. #1
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    Statistic Help

    The mean is 100. Standard Deviation is 16 on a normal curve.

    The question is:
    If the distribution of mental ability scores is normal, the middle 68 percent of the scores should lie between what two scores?
    answer: 84 to 116. How do you find this?

    The next question is:
    The middle 96 percent of the mental ability scores should be between what two values?
    answer: 68 to 132

    Its killing me.
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  2. #2
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    I think 'they' expect you to just learn these two facts.

    68% lie between mean - 1 sd and mean + 1 sd

    So you get 100-16 to 100+16

    95% lie between mean -2 sd and mean + 2 sd
    So you get 100-32 to 100+32
    Attached Thumbnails Attached Thumbnails Statistic Help-normal-iq.jpg  
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  3. #3
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    Thank you very much

    You explained it in two lines. The book is awful.
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  4. #4
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    Quote Originally Posted by CavalryScout View Post
    You explained it in two lines. The book is awful.
    Maybe the book used a method that:

    1. Gets a more accurate answer, and

    2. Provides a template for answering questions like

    "If the distribution of mental ability scores is normal, the middle [40] percent of the scores should lie between what two scores?"

    You should realise that

    "68% lie between mean - 1 sd and mean + 1 sd"

    is a rough rule of thumb ("68-95-99.7 rule") - useful under certain circumstances.
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  5. #5
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    I'd just like to say I agree with everything Mr Fantastic said and promise to be a bit more careful in future.
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  6. #6
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    Quote Originally Posted by a tutor View Post
    I'd just like to say I agree with everything Mr Fantastic said and promise to be a bit more careful in future.
    Hey, it's no big deal. Where I was coming from is that sometimes a student gets an easy question that can be done using an easy method (often just a memorised rule), but when the question gets a bit trickier (like the example I gave) the student flounders becuase they have no general process to fall back on.

    Great to have you on board, by the way
    Last edited by mr fantastic; January 27th 2008 at 01:36 PM.
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