To construct a confidence interval for the difference between two population means 12, use the formula shown below when both population standard deviations areknown, and either both populations are normally distributed or both n130 and n230. Also, the samples must be randomly selected and independent.

x1x2zc

21n1+22n2<12

21n1+22n2

The descriptive statistics for the annual salaries from a random sample of microbiologists from two regions are shown below. Construct a95% confidence interval for the difference between the mean annual salaries.

x1=$105,020, n1=41, and 1=$8685; x2=$85,870, n2=37, and 2=$8685