1)An article reported that for a sample of43kitchens with gas cooking appliances monitored during a one-week period, the sample mean CO₂level (ppm) was 654.16, and the sample standard deviation was163.87.

(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 (b) Suppose the investigators had made a rough guess of166for the value ofsbefore collecting data. What sample size would be necessary to obtain an interval width of53ppm for a confidence level of 95%? (Round your answer up to the nearest whole number.) ( , ) kitchens

2)On the basis of extensive tests, the yield point of a particular type of mild steel-reinforcing bar is known to be normally distributed with= 100.The composition of the bar has been slightly modified, but the modification is not believed to have affected either the normality or the value of.

(a) Assuming this to be the case, if a sample of25modified bars resulted in a sample average yield point of8428lb, compute a 90% CI for the true average yield point of the modified bar. (Round your answers to one decimal place.)

,

lb

3)An article reported that for a sample of43kitchens with gas cooking appliances monitored during a one-week period, the sample mean CO₂level (ppm) was 654.16, and the sample standard deviation was163.87.(

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

(b) Suppose the investigators had made a rough guess of166for the value ofsbefore collecting data. What sample size would be necessary to obtain an interval width of53ppm for a confidence level of 95%? (Round your answer up to the nearest whole number.) kitchens