Assume that the helium porosity (in percentage) of coal samples taken from any p

Question

Assume that the helium porosity (in percentage) of coal samples taken from any particular seam is normally distributed with true standard deviation 0.79. (a Compute a 95% CI for the true average porosity of a certain seam if the average porosty for 21 specimens from the seam was 4 decimal places.) 5. Round your answers to two 4.51 , 5.19 b) Compute a 98% CI or true average porosity of another seam based on 17 specimens with a sample average por s o 456 Rou n your answers to two de amal places.) 4.11 , 5.01 c) How large a sample size is necessary if the width of the 95% interval is to be 472 Round your answer, up to the nearest whole number X specimens (d) What sample size is necessary to estimate true average porosity to within 0.2 with 99% confidence? (Round your answer up to the nearest whole number.) specimens

Explanation / Answer

c)

d)

for 95 % CI value of z= 1.9600 standard deviation = 0.79 margin of error E = 0.235 required sample size n=(z/E)2                                         = 44

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