# a) n = 81 and = 6.1 pounds b) n = 36 and = 7.0 pounds c) n = 9 and = 5.8 pounds a)

a) n = 81 and = 6.1 pounds b) n = 36 and = 7.0 pounds c) n = 9 and = 5.8 pounds a) In performing a t-test based on 21 observations, what are the critical values for a one-tailed test when α = 0.05? That is, what values of the tstat will give a one-sided P-value that is less than or equal to 0.05? What are the critical values for a two-tailed test at α = 0.05? a) Calculate a 95% confidence interval for the mean menstrual cycle length. b) Based on the confidence interval you just calculated, is the mean menstrual cycle length significantly different from 28.5 days at α = 0.05 (two sided)? Is it significantly different from μ = 30 days at the same α-level? Explain your reasoning. (Section 10.4 in your text considered the relationship between confidence intervals and significance tests. The same rules apply here.) a) Calculate delta values for each city. Then construct a stemplot of these differences. Interpret your plot. b) What percentage of cities showed an improvement in their cavity-free rate? c) Estimate the mean change with 95% confidence.