SOLUTION: A plastics company wishes to estimate the mean impact strength of a spool. How many spools should the company test if it wishes to have an interval width of 30 psi with 95% confide

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Question 615452: A plastics company wishes to estimate the mean impact strength of a spool. How many spools should the company test if it wishes to have an interval width of 30 psi with 95% confidence? Previous experince indicates that an acceptable estimate of standard deviation squared is 4900.
Answer by stanbon(75887) About Me  (Show Source):
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A plastics company wishes to estimate the mean impact strength of a spool. How many spools should the company test if it wishes to have an interval width of 30 psi with 95% confidence? Previous experince indicates that an acceptable estimate of standard deviation squared is 4900.
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If the CI width is 30, ME = 15
s = sqrt(4900) = 70
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n = [z*s/E]^2
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n = [1.96*70/15]^2 = 84 when rounded up
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Cheers,
Stan H.
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