Assume that the helium porosity in percentage of coal specimen taken from any pa

Question

Assume that the helium porosity in percentage of coal specimen taken from any particular seam is normally distributed with population standard deviation .85. How large of a sample size is necessary if the total width of a 95% confidence interval for z interval is to be .35 or less

Write base equation as well as plugging the values in

Assume that the helium porosity in percentage of coal specimen taken from any particular seam is normally distributed with population standard deviation .85. How large of a sample size is necessary if the total width of a 95% confidence interval for z interval is to be .35 or less

Write base equation as well as plugging the values in



Write base equation as well as plugging the values in

Explanation / Answer

we know that the CI is given as

Mean +- z*sd/sqrt(n) , so the width is

Mean + z*sd/sqrt(n) - Mean + z*sd/sqrt(n)

2*Z*sd/sqrt(n) = 0.35

so z = 1.96 , for 95% CI and sd = 0.85

2*1.96*0.85/0.35 = sqrt(n)

9.52 = sqrt(n)

n = 9.52^2 = 90.63

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