A geologist examines 28 seawater samples for mercury concent

A geologist examines 28 seawater samples for mercury concentration. The mean mercury concetration for the sample data is. 0.495 cc/cubic meter with a standard deviation of 0.069. Determine the 90% confidence interval for the population mean mercury concentratio. Assume the population is normally distributed. Find the crirtical value that should be used in constructing the confidence interval. Round answer to 3 decimal places

Solution

Given a=1-0.9=0.1, the critical value is Z(0.05) = 1.645 (from standard normal table)

So the lower bound is

xbar - Z*s/vn =0.495-1.645*0.069/sqrt(28) =0.474

So the upper bound is

xbar +Z*s/vn =0.495+1.645*0.069/sqrt(28) =0.516