5. Assume that the helium porosity (in percentage) of coal sam- ples taken from any particular seam is normally distributed with true standard deviation .75. a. Compute a 95% CI for the true average...

can u please ans the d part

Extracted text: 5. Assume that the helium porosity (in percentage) of coal sam- ples taken from any particular seam is normally distributed with true standard deviation .75. a. Compute a 95% CI for the true average porosity of a cer- tain seam if the average porosity for 20 specimens from the seam was 4.85. b. Compute a 98% CI for true average porosity of another seam based on 16 specimens witha sample average poros- ity of 4.56. c. How large a sample size is necessary if the width of the 95% interval is to be 40? d. What sample size is necessary to estimate true average porosity to within .2 with 99% confidence?