Differentiate the difference between point estimate and confidence interval, at the 95% confidence level. A company producing electrical liquid mosquito-repellent intends to determine its product's lifetime. Consider the following situations:
(a) Assume that the lifetime of the product follows normal distribution with population standard deviation of 9 hours. If 9 products are taken randomly as samples, then the sample mean would be 100 hours.
(b) Assume that the lifetime of product follows a normal distribution with unknown standard deviation. If 9 products are taken randomly as sample, then the sample mean would be 100 hours with sample standard deviation of 10 hours.