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war485
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Homework Statement
Suppose the porosity (in %) of samples taken from the ground found to be normally distributed with σ = 0.85 %
What sample size is necessary to estimate the true mean porosity to within 0.25
with 99% confidence?
Homework Equations
C.I. = confidence interval = mean +- z*σ*n^(-0.5)
n = (2*z*σ/w)^2
interval width = w
z = 2.575
The Attempt at a Solution
Not really sure what is meant by "... to within 0.25" maybe someone can help clarify this? Is it referring to the confidence interval width? Also, I thought that the confidence intervals do not estimate the true mean. I thought C.I. only estimates whether or not the other samples will have the same mean within the C.I. range.
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