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Math Help - Normal distribution and standard deviation?

  1. #1
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    Exclamation Normal distribution and standard deviation?

    100 studentes took a test on which the mean score was 73 with a variance of 64. a grade of A was given to all who scored 85 or better. Approximately how many A's were there, assuming scores were normally distributed?

    is there anyway to solve this other than using a normal distribution table? Like, is there a formula you can use to calculate the percentage just by looking at the sd? Thank you
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    Hello,
    Quote Originally Posted by Kalyn View Post
    100 studentes took a test on which the mean score was 73 with a variance of 64. a grade of A was given to all who scored 85 or better. Approximately how many A's were there, assuming scores were normally distributed?

    is there anyway to solve this other than using a normal distribution table? Like, is there a formula you can use to calculate the percentage just by looking at the sd? Thank you
    No, I don't think there is any...

    You'll have to make Z=\frac{X-73}{\sqrt{64}} and then find P(X>85)=P(Z>\tfrac{85-73}{\sqrt{64}})=\text{ look in the table}
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