Remember the data on puberty that you studied in the chapter on variability? Well, in the United States, the average age of menarche (first menstrual period) is 12.75 years. Now, let's suppose that residents who live near an abandoned chemical plant are concerned about the environmental effects on their children. Suppose that one concerned parent gathered the data on age of menarche for 20 residents who had lived in the area for at least six years before puberty. Summary data (in years) follow. Construct a 95 percent confidence interval about the mean. Explain what the data have to say about the resident's concern. In your explanation, refer to your confidence interval and the nation's average age of menarche.

EX = 224 EX2= 2,609