SOLUTION: A standard placement test has a mean of 115 and a standard deviation of 10. What is the minimum sample size required if we want to construct the 90% confidence interval with the ma

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Question 472065: A standard placement test has a mean of 115 and a standard deviation of 10. What is the minimum sample size required if we want to construct the 90% confidence interval with the margin of error 2 points?.
Answer by stanbon(75887) About Me  (Show Source):
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A standard placement test has a mean of 115 and a standard deviation of 10. What is the minimum sample size required if we want to construct the 90% confidence interval with the margin of error 2 points?.
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ME = z*s/sqrt(n)
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2 = 1.645*10/sqrt(n)
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sqrt(n) = [1.645*10/2]
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sqrt(n) = 8.225
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n = 68 when rounded up
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Cheers,
Stan H.