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1.Assume that the helium porosity (in percentage) of coal samples taken from any particular seam is...

1.Assume that the helium porosity (in percentage) of coal samples taken from any particular seam is normally distributed with true standard deviation σ = 0.8. A sample of 13 specimens from the seam produces average porosity 4.6.

The 90% confidence interval for the true average of helium porosity is:
(4.316    ,    4.884)
(4.235    ,    4.965)
(4.205    ,    4.995)

Tries 0/2

What is the minimum sample size required to estimate the true average porosity within 0.1 with 90% confidence?

694 173 174

2.A random sample of 25 adult females is used to calculate a 95% confidence interval for the true mean weight of female adults. Which of the following would reduce the margin of error for the confidence interval? Choose the best answer.
sample size 20
99% confidence and sample size 20
99% confidence level and sample size 30
sample size 30
99% confidence level

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