1. A sample of ultimate tensile strength observations (ksi) was taken. Use the accompanying descriptive statistics output from Minitab to calculate a 99% lower confidence bound for true average ultimate tensile strength, and interpret the result. (Round your answer to two decimal places.)

N	Mean	Median	TrMean	StDev	SE Mean	Minimum	Maximum	Q1	Q3
153	135.35	135.36	135.37	4.43	0.36	121.20	149.60	131.95	136.35

We are 99% confident that the true average ultimate tensile strength is greater than

2. An article reported that for a sample of59kitchens with gas cooking appliances monitored during a one-week period, the sample mean CO₂level (ppm) was 654.16, and the sample standard deviation was165.91.(a) Calculate and interpret a 95% (two-sided) confidence interval for true average CO₂level in the population of all homes from which the sample was selected. (Round your answers to two decimal places.)

,

ppm Interpret the resulting interval.We are 95% confident that the true population mean lies above this interval.We are 95% confident that this interval does not contain the true population mean. We are 95% confident that the true population mean lies below this interval.We are 95% confident that this interval contains the true population mean. (b) Suppose the investigators had made a rough guess of183for the value ofsbefore collecting data. What sample size would be necessary to obtain an interval width of50ppm for a confidence level of 95%? (Round your answer up to the nearest whole number.) kitchens

3.Assume that the helium porosity (in percentage) of coal samples taken from any particular seam is normally distributed with true standard deviation 0.71.

(c) How large a sample size is necessary if the width of the 95% interval is to be 0.39? (Round your answer up to the nearest whole number.)