The concentration of benzene was measured in units of milligrams per liter for a simple random sample of five specimens of untreated wastewater produced at a gas field. The sample mean was 7.8 with a sample standard deviation of 1.4. Seven specimens of treatment wastewater had an average benzene concentration of 3.2 with a standard deviation of 1.7. It is reasonable to assume both samples come from populations that are approximately normal. Required:
Can you conclude that the mean benzene concentration is less in treated water than in untreated water? Use the a=0.05 level of significance.