Contaminated water: The concentration of benzene was measured in units of milligrams per liter for a simple random sample of six specimens of untreated wastewater produced at a gas field. The sample...

Contaminated water: The concentration of benzene was measured in units of milligrams per liter for a simple random sample of six specimens of untreated wastewater produced at a gas field. The sample mean was

with a sample standard deviation of

. Eight specimens of treated wastewater had an average benzene concentration of

with a standard deviation of

. It is reasonable to assume that both samples come from populations that are approximately normal. Construct a


confidence interval for the reduction in benzene concentration after treatment. Use tables to find the critical value and round the answers to at least one decimal place.