answer all questions with explanation

3. (20 pts) Suppose that the standard deviation of a particular brand of television LED screen is known to be o = 500 hours but the mean life is unknown. The operating life of the LED screens is approximately normally distributed. For sample size of 20 the mean operating life is 8800 hours. Determine a) the 95% and b) 85% confidence interval for the mean. 4. (20 pts) Suppose that the operating life of the LED screens in Problem 3 is not normally distributed due to a variation in the manufacturing process. a) What is the minimum number of samples required to determine the mean? b) Determine the 90% confidence interval for the mean