Assume that the helium porosity in percentage of coal samples taken from any particular seam is normally distributed with true standard deviation 0 73 a Compute a 95 CI for the true average porosity of a certain seam if the average porosity for 24 specimens from the seam was 4 85 Round your answers to two decimal places b Compute a 98 CI for true average porosity of another seam based on 18 specimens with a sample average porosity of 4 56 Round your answers to two decimal places c How large a sample size is necessary if the width of the 95 interval is to be 0 3 Round your answer up to the nearest whole number specimens d What sample size is necessary to estimate true average porosity to within 0 24 with 99 confidence Round your answer up to the nearest whole number specimens