Assume that the helium porosity (in percentage) of coal samples 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 certain 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 with a sample average porosity 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?

STATS 241 Week 6 Chapter 6 ⇒Continuous random variables- take up an infinite amount of space in an interval on the real number l ine ⇒Normal distribution- used mostly with continuous probability distribution ⇒Continuous probability d istribution: ★ The probability that a random variable is between two values ★ Given by the area under the graph of probability distribution between the two values ★ The probability that a continuous random variable is exactly a specific number is zero ★ Total pr