SOLUTION: A standard placement test has a mean of 115 and a standard deviation of  = 10. Determine the minimum sample size if we want to be 90% certain that we are within 2 points of
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Question 324064: A standard placement test has a mean of 115 and a standard deviation of = 10. Determine the minimum sample size if we want to be 90% certain that we are within 2 points of the true mean. Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website! A standard placement test has a mean of 115 and a standard deviation of = 10. Determine the minimum sample size if we want to be 90% certain that we are within 2 points of the true mean.
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Since E = zs/sqrt(n)
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sqrt(n) = zs/E
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So, n = [zs/E]^2
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z for 90% CI = 1.645
s = 10
E = 2
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n = [1.645*10/2]^2 = 68 when rounded up
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Cheers,
Stan H.
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