The service life of a battery used in a cardiac pacemaker is assumed to be normally distributed. A random sample of 10 batteries is subjected to an accelerated life test by running them continuously at an elevated temperature until failure, and the following lifetimes (in hours) are obtained: 25.5, 26.1, 26.8, 23.2, 24.2, 28.4, 25.0, 27.8, 27.3, and 25.7.
(a) The manufacturer wants to be certain that the mean battery life exceeds 25h. What conclusions can be drawn from these data (use alpha=.05) ?
(b)Using the data, construct a 95% lower confidence interval on mean battery life. Why would the manufacturer be interested in a one-sided confidence interval?