A sample of 87 one-year-old spotted flounder had a mean length of 119.86 millimeters with a sample standard deviation of 16.66 millimeters, and a sample of 123 two-year-old spotted flounder had a mean length of 136.96 millimeters with a sample standard deviation of 27.21 millimeters. Construct a 95% confidence interval for the mean length difference between two-year-old flounder and one-year-old flounder. Let 1 denote the mean length of two-year-old flounder and round the answers to at least two decimal places.

A 95% confidence interval for the mean length difference, in millimeters, between two-year-old flounder and one-year-old flounder is ? <1< ? .

Contaminated water: The concentration of benzene was measured in units of milligrams per liter for a simple random sample of seven specimens of untreated wastewater produced at a gas field. The sample mean was 7.7 with a sample standard deviation of 1.3. Nine specimens of treated wastewater had an average benzene concentration of 3.5 with a standard deviation of 1.5. It is reasonable to assume that both samples come from populations that are approximately normal. Construct a 95% 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.

A 95% confidence interval for the reduction in benzene concentration after treatment is ?< u1-u2