An investment banker would like to determine the percentage of new clients who will make the certain kind of investment. If she wants the sampling error of new greater than 2.5% and confidence level of 90%, how many clients must she sample? What sample size is needed for 85% confidence level?
A manufacturer bonds a plastic coating in metal surface. A random sample of nine observations n the thickness of this coating is taken from the week's output, and the thickness in millimeters are follows:
19.8 21.2 18.6 20.4 21.6 19.8 19.9 20.3 20.8
Supposing normality, find out a 90% confidence interval for the population variance.