How large a sample size is necessary if the width of the 95

Assume that the helium porosity of coal samples taken from any particular seam is Normally distributed with true standard deviation 0.75.

a. Compute a 95% CI for the true average porosity of a certain seam if the average porosity for 20 specimens from the seam was 4.85.

b. Compute a 98% CI for true average porosity of another seam based on 16 specimens with a sample average of 4.56.

c. How large a sample size is necessary if the width of the 95% interval is to be 0.40?

d. What sample size is necessary to estimate the true average porosity to within 0.2 with 99% confidence?

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How large a sample size is necessary if the width of the 95 : assume that the helium porosity of coal samples taken from any particular seam is normally distributed with true

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Find the 95 confidence interval for the difference between : find the 95 confidence interval for the difference between two means based on this information about two samples.

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