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February 27th, 2016, 06:16 PM   #1
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Stats practice question

I have no idea where to even begin

The mean grade on a statistics quiz is 8 with a standard deviation of 0.5. What percent of the scores will be higher than 9? Assume the data is symmetrical.
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February 27th, 2016, 06:24 PM   #2
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Can you assume the distribution is normal? If so, let X be the grade somebody gets on the test. $\displaystyle X \sim N(\mu = 8, \sigma = 0.5)$.

$\displaystyle P(X > 9) = P(\frac{X - \mu}{\sigma} > \frac{9 - 8}{0.5}) = P(Z > 2) \approx 2.5\% $ (the exact answer will depend on the statistical table that your teacher gave you, but if you don't have a table, $\displaystyle 0.5 - \frac{0.95}{2} = 0.025$ is what you should answer).

Last edited by 123qwerty; February 27th, 2016 at 06:27 PM. Reason: Clarify
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