Assume that the helium porosity (in percentage) of coal samplestaken from any particular seam is normally distributed with truestandard deviation 0.77.
(a) Compute a 95% CI for the true average porosity of a certainseam if the average porosity for 16 specimens from the seam was4.85. (Round your answers to two decimal places.)
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(b) Compute a 98% CI for true average porosity of another seambased on 12 specimens with a sample average porosity of 4.56.(Round your answers to two decimal places.)
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(c) How large a sample size is necessary if the width of the 95%interval is to be 0.49? (Round your answer up to the nearest wholenumber.)
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(d) What sample size is necessary to estimate true average porosityto within 0.23 with 99% confidence? (Round your answer up to thenearest whole number.)
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