Selenium A small amount of the trace element selenium, 50-200 micrograms (mg) per day, is considered essential to good health. Suppose that random samples of n1 =n2 = 30 adults were selected from two regions of the United States and that a day's intake of selenium, from both liquids and solids, was recorded for each person. The mean and standard deviation of the selenium daily intakes for the 30 adults from region 1 were x1 = 167.1 and s1 =24.3 mg, respectively. The corresponding statistics for the 30 adults from region 2 were x2 = 140.9 and s2 =17.6. Find a 95% confidence interval for the difference in the mean selenium intakes for the two regions. Interpret this interval.