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10 items were randomly sampled with a mean diameter of 8.29mm and a sd of 1.314mm....

10 items were randomly sampled with a mean diameter of 8.29mm and a sd of 1.314mm.
what is the sample size needed to estimate the true avg diameter to within 0.25mm with 95% confidence?
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Answer #1

Solution :

Z\alpha/2 = Z0.025 = 1.96  

sample size = n = [Z\alpha/2* \sigma / E] 2

n = [ 1.96 * 1.314 / 0.25 ]2

n = 106.12

Sample size = n = 107

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