8-14. The life in hours of a 75-watt light bulb is known to be normally distributed with σ=25 hours. A random sample of 20 bulbs has a mean life of xˉ =1014 hours. (a) Construct a 95% two-sided confidence interval on the mean life. (b) Construct a 95\% lower-confidence bound on the mean life. Compare the lower bound of this confidence interval with the one in part (a). 8-5. A random sample has been taken from a normal distribution and the following confidence intervals constructed using the same data: (38.02,61.98) and (39.95,60.05) (a) What is the value of the sample mean? (b) One of these intervals is a 95%CI and the other is a 90% CI. Which one is the 95%CI and why?