Two Confidence Interval Six measurements were made of the concentration (in percent) of ash in a certain variety of spinach. The sample mean was 19.35 and the sample standard deviation was 0.577. a Find a 95% confidence interval for the concentration of ash. b Find a 98% confidence interval for the concentration of ash. c If the six measurements had been 19.26, 19.50, 19.64, 18.26, 19.93, 19.51, would the confidence intervals in parts (a) and (b) be valid? Explain. Question Three Confidence Interval In a sample of 100 boxes of a certain type, the average compressive strength was 6230 N and the standard deviation was 221 N. a Find a 95% confidence interval for the mean compressive strength of boxes of this type. b Find a 99% confidence interval for the mean compressive strength of boxes of this type. c An engineer claims that the mean strength is between 6205 and 6255 N. With what level of confidence can this statement be made? d Approximately how many boxed must be sampled so that a 95% CI will specify the mean to within 25N